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Gravity
Terms in this set (98)
A vector is a quantity that has
magnitude and direction
A scalar is a quantity that has only
magnitude
When representing velocity as a vector
the direction of the arrow shows the direction of motion, the length of the arrow is drawn to scale, the length of the arrow represents the magnitude of the speed
In order to find the components of a resultant vector, you should
calculate the sine of the angle multiplied by the magnitude for the y, draw the vectors with correct magnitude and orientation, calculate the cosine of the angle multiplied by the magnitude for the x
The horizontal component of a projectile's velocity is independent of
the vertical component of its velocity
At the instant a ball is thrown horizontally with a large force, an identical ball is dropped from the same height. Which ball hits the ground first?
Neither - they both hit the ground at the same time
At what part of the path does a projectile have minimum speed in the vertical direction?
At the top of its path
A cannonball is launched from the ground at an angle of 30 degrees above the horizontal and a speed of 20 m/s. Ideally (no air resistance) the ball will land on the ground with a speed of
20m/s
An object is dropped and falls freely to the ground with an acceleration of 9.8 m/s2. If it is thrown upward at an angle instead, its acceleration would be
9.8 m/s2 downward
What is the resultant displacement of a man who walked 4 meters east and then 3 meters north?
5 meters
The law of inertia states that an object
will continue moving at the same velocity unless an outside force acts on it, will continue moving in a straight line unless an outside force acts on it, that is not moving will never move unless a force acts on it, at rest will remain at rest unless acted on by an outside force
The law of inertia applies to
both moving and nonmoving objects
A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. The reason this can be done is that
the milk carton has inertia
one object has twice as much mass as another object. The first object also has twice as much
inertia
A 10-N force and a 30-N force act on an object in opposite directions What is the net force on the object?
20 N
Friction is a force that always acts
opposite to the object's motion
Which has more mass, a kilogram of feathers or a kilogram of iron?
Neither - they both have the same mass
How much does a 1 kg bag of nails weigh?
9.8 N
A 10-N force and a 30-N force act in the same direction on an object. What is the net force on the object?
40 N
A force can be simply defined as a push a pull.
Ture
The SI unit of mass is the Newton.
False, kilogram
Inertia is the property that every material object has; inertia resists changes in an object's state of motion.
True
The combination of all the forces that act on an object is called the net force.
True
The force that supports the weight of a book lying at rest on a tabletop is called a normal force.
True
Whenever an object exerts a force on another object, the second object exerts a force of the same magnitude, but in the opposite direction to that of the first object.
True (Newton's 3rd Law)
Impulse is defined as the force exerted on an object divided the time it lasts.
False, multiplied
When two objects collide and completely stick together, the collision is said to be elastic.
False, inelastic
When a baseball player follows through when hitting the ball, the contact time with the ball is longer.
True
If a net force acts on a system, the system's momentum will change.
True, Ft = m(change in V)
Any force that causes an object to move in a circular path is called a centripetal force.
True
The amount of potential energy an object has depends on the path taken to get to a certain height.
False
Energy is changed from one form to another with no net loss or gain.
True
A person weighs 500 N. What is the mass of the person?
Divide weight by 9.8
Accelerations are produced by
forces
How does acceleration of an object change in relation to it's mass? It is
inversely proportional
A girl pulls on a 10-kg wagon with a constant net fore of 30 N. What is the wagon's acceleration?
a = force/mass
Aunt Minnie throws a rock downward, and air resistance is negligible. The acceleration of the rock compared to being dropped is
the same
If the force action on a cart doubles, what happens to the cart's acceleration?
it doubles; F is proportional to a
Suppose a cart is being moved by a force. if suddenly a load is dumped into the cart so that the cart's mass doubles, what happens to the cart's acceleration?
it halves
A 10-N falling object encounters 4 N of air resistance. The magnitude of the net force on the object is
6 N
A car has a mass of 1000 kg and accelerates at 2 m/s^2. What is the magnitude of the force action on the car?
2000 N
A tow truck exerts a force of 3000 N on a car, accelerating it at 2 m/s^2. What is the mass of the car?
1500 kg
A high school student hits an nail with a hammer. During the collisions, there is a force
on the nail and also on the hammer
A player hits a ball with a bat. The action force is the impact of the bat against the ball. What is the reaction to this force?
The force of the ball against the bat
The momentum of an object is defined as the object's
mass times its velocity
Which has more momentum, a large truck moving at 30 mph or a small truck moving at 30 mph?
The large truck
Compared to a sports car moving at 30 mph, the same sports car moving at 60 mph has
twice as much momentum
If the momentum of an object changes and its mass remains constant,
it is acceleration, there is a force action on it, its velocity is changing
In order to increase the final momentum of a golf ball, we could
increase the force action on it, follow through when hitting the ball, increase the time of contact with the ball, and swing as hard as possible
The reason airbags are used in cars is that they
increase the time of impact in a collision
Which of the following has the largest momentum?
A pickup truck traveling down the highway
A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collisions is
smaller
A 2 kg ball is thrown at 3 m/s. What is the ball's momentum?
6 kg m/s
A 4 kg ball has a momentum of 12 kgm/s. What is the ball's speed?
3 m/s
A 8 kg blob of clay moving horizontally at 2 m/s hits a 4 kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision?
1.3 m/s
A 40 kg football player leaps through the air to collide with and tackle a 60 kg player heading toward him, also in the air. if the 40 kg player is heading to the right a 7 m/s, and the 60 kg player is heading toward the left a 3 m/s, what is the speed and direction of the tangled players?
1 m/s to the right
One possible unit of speed is
meters per second, miles per hour, kilometers per hour
When you look at the speedometer in a moving car, you can see the car's
instantaneous speed
Acceleration is defined as the change in
velocity decided by the time interval
In the absence of air resistance, objects fall at a constant
acceleration
A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always
directed downward
A ball is through straight up. At the top of its path its acceleration is
about 10 m/s^2
If a projectile is fired straight up at a speed of 10 m/s, the total time to return to its starting point is about
2 sec
The ability to do work is a definition of
energy
Mechanical energy is the sum of
potential and kinetic energy
energy is measured in what units?
Joules
Energy of an object caused by its motion
kinetic
When you raise an object away from the earth, the potential energy of the object relative to the earth's surface
increases
Net work done on an object is equal to
change in the kinetic energy
Conservation of energy states the total amount of energy in an isolated, closed system
must remain constant
Kinetic energy increases by a factor of 9 if the velocity of an object is multiplied by
3
if positive net work is done on an object, the kinetic energy increased causing the object to
speed up
Which of the following are types of potential energy we discussed
Gravitational
The amount of potential energy an object has depends on
Vertical path taken to get to a certain height
Potential energy is the energy an object has because of its
position
The amount of potential energy possessed by an elevated object is equal to
the work done in lifting it
What happens to the energy in a pendulum as it swings back and forth?
Potential energy is transformed into kinetic energy and back into potential energy constantly
An object that has linear kinetic energy must
have a velocity
As a rocket moves away from the earth's surface, the rocket's weight
decreases
A ball is whirled around in a circle. What happens to the centripetal acceleration if the velocity is tripled?
It increases by a factor of 9
If a string breaks that holds a whirling rock in its circular path, what causes the rock to now move in a straight-line path?
inertia
What is the centripetal force that keeps a satellite in orbit above the earth?
The force of gravtiy
The period of rotation for an object moving in a circular path is
the time it takes the object to go around once
A space ship is traveling to the moon. At what point is it beyond the pull of the earth's gravitational field?
It is never beyond the pull of the earth's gravity
According to Newton's law of universal gravitation, the force of gravitational attraction between any two masses is directly proportional to
the product of two masses
When a car goes around a curve, what force keeps the car on the road?
The force of friction between the road and tires
In the universal gravitation equation, the letter G stands for
universal gravitation constant
According to Newton's law of universal gravitation, as the distance between two bodies increases, the force of gravity between the bodies
decreases
One basic definition of energy is that it is
the ability to do work
energy and work are both measured in
joules
As an object falls towards earth, the potential energy of the object ____ relative to the earth's surface
decreases
A change in the kinetic energy of an object is equal to the
net work done on the object
The total amount of energy in an isolated, closed system
remains constant
If the velocity of an object doubles, the amount of kinetic energy
quadruples
A rock whirled on the ned of a string moves in a circle because
the string continually pulls inward on the rock
The amount of potential energy possessed by an elevated object is equal to
the work done in lifting it
As a pendulum swings back and forth
potential energy is transformed into kinetic energy, at the lowest part of its swing its energy is all kinetic, and the end points of its swing its energy is all potential, kinetic energy is transformed into potential energy
An object that has linear kinetic energy must be
moving
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