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AP Physics Chapter 6
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Gravity
Terms in this set (39)
What is the correct unit of work expressed in SI ?
Kg m2/s2
Can work be done on a system if there is no motion?
No, because of the way work is defined.
If you push twice as hard against a stationary brick wall, the amount of work you do
remains constant at zero
A 50-N object was lifted 2.0 m vertically and is being held there. How much work is being done inholding the box in this position?
0 J
f you walk 5.0 m horizontally forward at a constant velocity carrying a 10-N object, the amount of work you do is
zero
A container of water is lifted vertically 3.0 m then returned to its original position. If the total weight is30 N, how much work was done
no work was done
Does the centripetal force acting on an object do work on the object?
No, because the force and the displacement of the object are perpendicular.
You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up withthe sign of the work done by gravity while it goes down.
Work is - on the way up and + on the way down
The area under the curve, on a Force versus position (F vs. x) graph, represents
work
On a plot of Force versus position (F vs. x), what represents the work done by the force F?
the area under the curve
The quantity 1/2 mv2 is
the kinetic energy of the object
If the net work done on an object is positive, then the object's kinetic energy
increases
If the net work done on an object is negative, then the object's kinetic energy
decreases
If the net work done on an object is zero, then the object's kinetic energy
remains the same
A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement istrue about the truck's kinetic energy compared to that of the car?
The truck has 8 times the kinetic energy of the car
Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J,compared to car K is
2 to 1
An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?
1/4
A brick is moving at a speed of 3 m/s and a pebble is moving at a speed of 5 m/s. If both objects havethe same kinetic energy, what is the ratio of the brick's mass to the rock's mass?
25 to 9
A 4.0-kg mass is moving with speed 2.0 m/s. A 1.0-kg mass is moving with speed 4.0 m/s. Bothobjects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?
Both travel the same distance.
You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?
It would have skidded 4 times farther.
A planet of constant mass orbits the Sun in an elliptical orbit. Neglecting any friction effects, whathappens to the planet's kinetic energy?
It increases when the planet approaches the Sun, and decreases when it moves farther away
The quantity mgy is
the gravitational potential energy of the object.
The quantity 1/2 kx2 is
the elastic potential energy of the object.
Is it possible for a system to have negative potential energy?
Yes, since the choice of the zero of potential energy is arbitrary.
An object is released from rest a height
h above the ground. A second object with four times the massof the first if released from the same height. The potential energy of the second object compared to the first is
four times as much
A 0.200-kg mass attached to the end of a spring causes it to stretch 5.0 cm. If another 0.200-kg mass isadded to the spring, the potential energy of the spring will be
4 times as much
The total mechanical energy of a system
is constant, only if conservative forces act.
An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U
K increases and U decreases
Describe the energy of a car driving up a hill
both kinetic and potential
A lightweight object and a very heavy object are sliding with equal speeds along a level frictionlesssurface. They both slide up the same frictionless hill. Which rises to a greater height?
They both slide to the same height.
Consider two masses m1and m2at the top of two frictionless inclined planes. Both masses start fromrest at the same height. However, the plane on which m1sits is at an angle of 30° with the horizontal,while the plane on which m2sits is at 60°. If the masses are released, which is going faster at the bottom of its plane ?
they both are going the same speed
A ball falls from the top of a building, through the air (air friction is present), to the ground below.How does the kinetic energy (K) just before striking the ground compare to the potential energy (U) at the top of the building?
K is less than U.
A ball drops some distance and gains 30 J of kinetic energy. Do not ignore air resistance. How muchgravitational potential energy did the ball lose?
more than 30 J
A ball drops some distance and loses 30 J of gravitational potential energy. Do not ignore air resistance. How much kinetic energy did the ball gain?
less than 30 J
The quantity Fd/t is
the power supplied to the object by the force.
What is the correct unit of power expressed in SI units
kg m2/s3
Of the following, which is not a unit of power?
watt/second
Compared to yesterday, you did 3 times the work in one-third the time. To do so, your power outputmust have been
9 times yesterday's power output
To accelerate your car at a constant acceleration, the car's engine must
develop ever-increasing power.
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