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Physics final

Terms in this set (60)

Two identical cars, car 1 and car 2, are moving in opposite directions on a straight road. The position of each car as a function of time is represented in the graph. What is the speed of the center of mass of the two-car system?
zero
The position as a function of time for two objects moving along a straight line is shown in the graph.
Which statement is true about the distances the two object have traveled at time tf?
Object 1 has traveled a greater distance
The position as a function of time for two objects moving along a straight line is shown in the graph.
At which of the following times do the two objects have the same velocity?
tc
Balls 1 and 2 are each thrown horizontally from the same height above level ground, but ball 2 has a greater initial velocity after leaving the thrower's hand. If air resistance is negligible, how do the accelerations of the balls and the times it takes them to hit the ground compare?
Acceleration a: equal ; Time to hit ground: equal
Block 1 slides rightward on the floor toward an ideal spring attached to block 2, as shown. At time t1, block 1 reaches the spring and starts compressing it as block 2 also starts to slide to the right. At a later time, t2, block 1 loses contact with the spring. Both blocks slide with negligible friction. Taking rightward as positive, which pair of graphs could represent the acceleration of block 2 and the center-of-mass acceleration of the two-block system?
Acceleration of Block 2: peaks between t1 and t2 / Center-of-mass acceleration: constant at zero
A block is projected up a frictionless plane with an initial speed v(o). The plane is inclined 30° above the horizontal. What is the approximate acceleration of the block at the instant that it reaches its highest point on the inclined plane
5 m/s^2 down the incline
A vertical spring launcher is attached to the top of a block and a ball is placed in the launcher, as shown in the figure. While the block slides at constant speed to the right across a horizontal surface with negligible friction between the block and the surface, the ball is launched upward. When the ball reaches its maximum height, what will be the position of the ball relative to the spring launcher?
Directly above the spring launcher
An engineer measures the velocity vv of a remote-controlled cart on a straight track at regular time intervals. The data are shown in the graph above. During which of the following time intervals did the cart return to its position at time t=0 s?
7s ≤ t < 10s
A blue sphere and a red sphere with the same diameter are released from rest at the top of a ramp. The red sphere takes a longer time to reach the bottom of the ramp. The spheres are then rolled off a horizontal table at the same time with the same speed and fall freely to the floor. Which sphere reaches the floor first?
Neither; the spheres reach the floor at the same time
Object A is released from rest at height h. At the same instant, object B is thrown downward from the same location. Which of the following graphs of speed of v as a function of time t is correct for the two objects?
same acceleration (same slope), B has higher initial value
The motion of a particle along a straight line is represented by the position versus time graph above. At which of the labeled points on the graph is the magnitude of the acceleration of the particle greatest?
C
A kitten sits in a lightweight basket near the edge of a table. A person accidentally knocks the basket off the table. As the kitten and basket fall, the kitten rolls, turns, kicks, and catches the basket in its claws. The basket lands on the floor with the kitten safely inside. If air resistance is negligible, what is the acceleration of the kitten-basket system while the kitten and basket are in midair?
The acceleration is directed downward with magnitude equal to g because the system is a projectile.
A hollow plastic ball is projected into the air. There is significant air resistance opposing the ball's motion, so the magnitude of the ball's acceleration is not equal to g. At time t, the ball is moving up and to the right at an angle of 45° to the horizontal, as shown above. Which of the following best shows the magnitude a and the direction of the ball's acceleration at time t ?
(down and to the left) a>g
A lion is running at constant speed toward a gazelle that is standing still, as shown in the top figure above. After several seconds, the gazelle notices the lion and accelerates directly toward him, hoping to pass the lion and force him to reverse direction. As the gazelle accelerates toward and past the lion, the lion changes direction and accelerates in pursuit of the gazelle. The lion and the gazelle eventually each reach constant but different speeds. Which of the following sets of graphs shows a reasonable representation of the velocities of the lion and the gazelle as functions of time?
lion's velocity starts below x-axis and changes direction to go above x-axis. gazelle's velocity starts zero and increases in the positive direction
The graphs above represent the position x, velocity v, and acceleration a as a function of time t for a marble moving in one dimension. Which of the following could describe the motion of the marble?
rolling up a ramp and then rolling back down
Blocks X and Y are glued together and released from rest on a ramp with negligible friction, as shown in trial 1. The blocks are then separated and connected by a light spring, as shown in trial 2. The spring is compressed and the blocks are again released from rest on the ramp. Immediately after the blocks are released, is the net force on the two-block system the same or different between trial 1 and trial 2? Immediately after the blocks are released, is the net force on block Y the same or different between trial 1 and trial 2?
Force on the system: the same / Force on block y: different
Two students need to move two identical boxes of mass M0 across a room where friction between the floor and the boxes cannot be neglected. One student moves the first box by pushing with a force of magnitude F0 at an angle θ from the horizontal, as shown in the figure for scenario 1. The other student moves the second box by pulling with a force of magnitude F0 at the same angle θ from the horizontal, as shown in the figure for scenario 2.
(F0cos(θ) - mu(M0g-F0sin(θ))/M0
In Figure 1, cart Y is connected to cart X by a tight string and is also connected to the hanging block of mass m0m0 by a light string that passes over a pulley. Figure 2 shows a system that is identical except for one change: cart Y and X are connected by a spring at its equilibrium length. Both systems are released from rest. Is the hanging block's acceleration as a function of time the same in both systems, and why or why not?
No, because the tension in the string connected to the block is constant in one system but not in the other.
A vehicle lands on Mars and explores its surface. The average gravitational field on the surface of Mars is 3.7 N kg . The weight of the vehicle is defined as the gravitational force exerted on it. Which of the following statements are true about the vehicle's weight? Select two answers.
The vehicle's weight increased while it was descending to the surface of Mars; The vehicle weighs less on the surface of Mars than on the surface of Earth.
In a lab, a block weighing 80 N is attached to a spring scale, and both are pulled to the right on a horizontal surface, as shown above. Friction between the block and the surface is negligible. What is the acceleration of the block when the scale reads 32 N?
4.0 m/s^2
A 50.0 N box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.50, and the coefficient of kinetic friction is 0.30. A horizontal 20.0 N force is then exerted on the box. The magnitude of the acceleration of the box is most nearly
0 m/s^2
On Earth, when a box slides across a horizontal board, the board exerts a frictional force of magnitude F0F0 on the box. The board and the box are moved to a planet with twice the radius but one-third the mass of Earth. When the box slides across the board, the frictional force exerted by the board on the box is now
(1/12)F0
A person is running on a track. Which of the following forces propels the runner forward?
The force of friction exerted by the ground on the person
Three identical blocks each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a frictionless incline. Block C is projected horizontally with an initial speed v.
Which block takes the longest time to reach the ground?
Block B
Four different constant forces are exerted on a 2.0 kg object. The figure represents the magnitude and direction of each force. If the object is initially at rest, how long will it take the object to reach a speed of 2.0 m/s?
4.0s
At time t = 0 two figure skaters are moving together over ice with negligible friction, as shown above. Skater 1, represented by the large black dot, is twice as massive as skater 2, represented by the gray dot. At t = 2 s the skaters push off of one another. The location of skater 1 is shown at t = 4 s . At t = 4 s , skater 2 is located at which of the labeled points?
point d
A 2 kg block, starting from rest, slides 20 m down a frictionless inclined plane from X to Y, dropping a vertical distance of 10 m as shown above.
The speed of the block at point Y is most nearly
14 m/s
Two identical blocks A and B are connected by a lightweight rope. Block A is pulled to the right by a constant force F0. The blocks are moving to the right across a rough surface and approach point P, where the rough surface transitions to a surface with negligible friction. How does the tension, T, in the rope connecting the blocks change, if at all, as block A passes point P?
T increases
Carts 1 and 2 are initially moving toward each other, as shown in the top figure. The carts collide and afterward are both moving to the right, as shown in the bottom figure. If the positive direction is to the right, which of the following best represents the force exerted on each cart by the other during the collision as a function of time?
cart 2 positive cart 1 negative reflected across x-axis
A box of mass m is released from rest and accelerates down a ramp that is at an angle θ to the horizontal, as shown. The coefficient of kinetic friction between the box and the ramp is μ. As the box is sliding down the ramp, how are the magnitudes of the horizontal and vertical components of the box's velocity changing, if at all?
Horizontal component: increasing / Vertical component: increasing
A meteoroid is in a circular orbit 600 km above the surface of a distant planet. The planet has the same mass as Earth but has a radius that is 90 % of Earth's (where Earth's radius is approximately 6370 km).
The acceleration of the meteoroid due to the gravitational force exerted by the planet is most nearly
10 m/s^2 toward the center of the planet
The toy car shown in the figure above enters the vertical circular loop with an initial velocity and moves completely around the loop without friction. If the car has no means of self-propulsion, which of the following is true of the car's acceleration at the instant it is at point P ?
It has components both downward and toward the center of the circle.
An object has a weight W when it is on the surface of a planet of radius R. What will be the gravitational force on the object after it has been moved to a distance of 4R from the center of the planet?
(1/16)W
A new planet is discovered that has twice the Earth's mass and twice the Earth's radius. On the surface of this new planet, a person who weighs 500 N on Earth would experience a gravitational force of
250 N
Planet X has twice Earth's mass and three times Earth's radius. The magnitude of the gravitational field near Planet X's surface is most nearly
2 N/kg
A planet with half Earth's mass and half Earth's radius is discovered. What would an astronaut who weighs 800 N on Earth weigh on the planet?
1600 N
A rock attached to a string swings in a vertical circle, as shown above, with negligible air resistance. Which of the following diagrams could correctly show all the forces on the rock when the string is in the position above?
Tensile force towards the center, gravitational force down
An amusement park ride consists of a large vertical wheel of radius R that rotates counterclockwise on a horizontal axis through its center, as shown above. The cars on the wheel move at a constant speed v. Points A and D represent the position of a car at the highest and lowest point of the ride, respectively. A person of weight Fg sits upright on a seat in one of the cars. As the seat passes point A, the seat exerts a normal force with magnitude 0.8Fg on the person. While passing point A, the person releases a small rock of mass m, which falls to the ground without hitting anything.
What is the normal force exerted on the rider when passing point D?
1.2 N
Planet 1 orbits Star 1 and Planet 2 orbits Star 2 in circular orbits of the same radius. However, the orbital period of Planet 1 is longer than the orbital period of Planet 2. What could explain this?
Star 1 has less mass than Star 2.
A block released from rest at position A slides with negligible friction down an inclined track, around a vertical loop, and then along a horizontal portion of the track, as shown above. The block never leaves the track.
Which of the following is true of the net force on the block when it is at position C ?
It has components both to the left and vertically downward.
A block released from rest at position A slides with negligible friction down an inclined track, around a vertical loop, and then along a horizontal portion of the track, as shown above. The block never leaves the track.
The gravitational potential energy and the kinetic energy of the block are most nearly equal at which position? (Consider the potential energy to be zero at position B.)
C
A newly discovered planet is found to have density 2/3 PE and radius 2RE, where pE and RE are the density and radius of Earth, respectively. The surface gravitational field of the planet is most nearly
13 N/kg
Two solid spheres of radius R made of the same type of steel are placed in contact, as shown in the figures above. The magnitude of the gravitational force that they exert on each other is F1. When two other solid spheres of radius 3R made of this steel are placed in contact, what is the magnitude of the gravitational force that they exert on each other?
81F1
The figures show a cart moving over the top of a hill (Case 1), moving at the bottom of a dip (Case 2), and moving at the top of a vertical loop (Case 3). In each case, the normal force acting on the car is Fn and the weight of the car is Fg. In which case is it always true that Fn>Fg, and in which case is it always true that Fn<Fg?
Fn>Fg always: Case 2 / Fn<Fg always: Case 1
A bus is initially traveling north at a constant speed, as shown in the figure above. As the bus starts to make a left turn without changing speed, a passenger notices that a box on the floor starts sliding toward the right side of the bus. Which of the following top views of the box, when correctly labeled, would best represent all of the horizontal forces exerted on the box as it starts sliding?
arrow pointing towards center of turn (representative of friction)
A 100 kg cart goes around the inside of a vertical loop of a roller coaster. The radius of the loop is 3 m and the cart moves at a speed of 6 m/s at the top. The force exerted by the track on the cart at the top of the loop is
200 N
A rocket is continuously firing its engines as it accelerates away from Earth. For the first kilometer of its ascent, the mass of fuel ejected is small compared to the mass of the rocket. For this distance, which of the following indicates the changes, if any, in the kinetic energy of the rocket, the gravitational potential energy of the Earth-rocket system, and the mechanical energy of the Earth-rocket system?
Rocket Kinetic Energy: Increasing / System Gravitational Potential Energy: Increasing / System Mechanical Energy: Increasing
A person holds a book at rest a few feet above a table. The person then lowers the book at a slow constant speed and places it on the table. Which of the following accurately describes the change in the total mechanical energy of the Earth-book system?
The total mechanical energy decreases, because the person does negative work on the book by exerting a force on the book in the direction opposite to its displacement.
Two frictionless lab carts start from rest and are pushed along a level surface by a constant force. Students measure the magnitude and duration of the force on each cart, as shown in the partially completed data table above, and calculate final kinetic energy and momentum. Which cart has a greater kinetic energy at the end of the push?
The 1kg cart
A vertical spring has unstretched length L0, as shown in Figure 1. A block is attached to the top of the spring and slowly lowered until it is at rest and the spring has length Leq, as shown in Figure 2. The block is then pushed down until the spring is compressed to length Lcomp, as shown in Figure 3, and then released. After release, at what height will the kinetic energy of the block be maximum?
Leq
A cart is moving on a level track in the positive x-direction. A force acting parallel to the x-axis is exerted on the cart. The graph above shows the net force exerted on the cart as a function of displacement. As the cart travels from x = 0 m to x = 4 m , what is the net change in the kinetic energy of the cart?
An increase of 10 J
A force F0 is applied continuously to a box initially at rest on a horizontal surface. The box slides with negligible friction for equal distances d1 and d2, as shown. How does the kinetic energy gained by the block over distance interval d2, ∆K2, compare to the kinetic energy gained over distance interval d1d1, ∆K1, and why?
∆K2=∆K1, because the applied force does the same work on the block over intervals d1d1 and d2d2.
A ball is suspended by a lightweight string, as shown in the figure above. The ball is displaced to position 1 and released. The four labeled positions are evenly spaced along the arc of the ball's motion. Between which adjacent pairs of positions is the change in kinetic energy of the ball greatest?
1 and 2
Three identical rocks are launched with identical speeds from the top of a platform of height 0 h . The rocks are launched in the directions indicated above.
Rock 1, of mass m, reaches a maximum height hmax after being launched. During the time between the instant rock 1 is launched from height h0 and the instant it returns to height h0, the work done on the rock by the gravitational force is
0
The graphs above show the magnitude F of a force exerted on an object as a function of the object's position x for two trials in an experiment. W1 and W2 are the work done on the object by force 1 and force 2, respectively. How do W1 and W2 compare, and why?
W1 < W2 , because the average value of force 1 is smaller than the average value of force 2.
The diagram shows the forces exerted on a block that starts from rest and speeds up as it moves down a rough incline near Earth's surface. Which of the following statements are true? Select two answers.
The total mechanical energy of the block-Earth system decreases as the block slides down the incline; The momentum of the block increases as the block slides down the incline.
Block A is set on a rough horizontal table and is connected to a horizontal spring that is fixed to a wall, as shown. Block A is then also connected to hanging block B by a lightweight string that passes over an ideal pulley, as shown. The friction force exerted on block A by the table is not negligible. The blocks are initially held at rest so that the spring is not stretched. When the blocks are released, hanging block B moves downward and block A on the table moves to the right until the system comes again to rest. Let E1 be the mechanical energy of the blocks-spring system, and let E2 be the mechanical energy of the blocks-spring-Earth system. How do these two energies change from when the blocks are held at rest to when the blocks come to rest again?
Increases Decreases
Two identical blocks are connected by a lightweight string that passes over a lightweight pulley that can rotate about its axle with negligible friction. The two-block system is released from rest and the blocks accelerate. Which of the following correctly relates the potential energy gained by the block 1-Earth system |∆U1||∆U1| to the potential energy lost by the block 2-Earth system |∆U2||∆U2| and provides correct evidence?
|∆U1|<|∆U2|, because the two-block system gains kinetic energy.
Two identical spaceships are moving through space both with speed v0. Both spaceships experience a net force of magnitude F0 over the same time interval. For spaceship 1, the net force acts in the same direction as the spaceship is moving; for spaceship 2, the net force is directed opposite to the spaceship's motion, causing spaceship 2 to slow down but not stop. For which spaceship, if either, does the kinetic energy change by a greater magnitude, and why?
Spaceship 1 will have a greater change in kinetic energy because the distance traveled is greater than that of spaceship 2.
A sled slides down a hill with friction between the sled and hill but negligible air resistance. Which of the following must be correct about the resulting change in energy of the sled-Earth system?
The sum of the kinetic energy and the gravitational potential energy changes by an amount equal to the energy dissipated by friction.
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