Download Answers2Work and PE Ques.cwk

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Work
1. When a force acts upon an object to cause a displacement of the object, it is said that
work was done upon the object. (true, false)
2. In order for a force to qualify as having done work on an object, there must be a
displacement and the force must cause the displacement. (true, false)
3. Tell which of the following involve work being done:
A teacher applies a force to a wall and becomes exhausted. (work, no work)
A book falls off a table and free falls to the ground.
(work, no work)
A rocket accelerates through space.
(work, no work)
A waiter carries a tray full of meals above his head by one arm straight across the
room at constant speed. (work, no work)
4. The equation for calculating work is : Work = Fd cos -0
5. The angle included in the equation for calculating work is measured as the angle between the force
and the displacement vector
6. A vertical force can never cause a horizontal displacement; thus, a vertical force does not
do work on a horizontally displaced object. (true, false)
7. A cart is pulled up a ramp by applying a force perpendicular to the incline. Work is done
by this force on the cart. (true, false)
8. Explain your answer to #7. Use the equation for calculating work to do so.
Fd cos90° = 0
9. Negative work is produced by a force directed opposite to the displacement
10. The standard metric unit for work is the joule
11. What three quantities must be known in order to be able to calculate the amount of
work?
force, displacement, angle between force and displacement
Potential Energy
12. Potential energy is the stored energy of position possessed by an object,
13. What are the two forms of energy of position?
gravitational potential energy and elastic potential energy
14. Gravitational potential energy is the energy stored in an object as the result
of its vertical position or height.
15. More massive objects raised to the same height as a lesser masses have
(less, equal, greater) gravitational potential energy.
16. The higher that an object is elevated, the (greater, less, height has no effect on )
the gravitational potential energy.
17. The equation used to calculate gravitational potential energy is mgh
18. A zero height position must be assigned from which to measure GPE.
(true, false)
19. Elastic potential energy is the energy stored in elastic materials as the result of their
stretching or compressing.
20. The amount of elastic potential energy stored in a device is related to the amount of stretch of
the device.
21. The equation used to calculate the amount of Fspring = spring constant x stretch = kx
22. If a spring is not stretched or compressed, then there is no elastic potential energy
stored in it. The spring is said to be at itsequilibrium position
23. The amount of elastic potential energy a spring possesses can be calculated by using
the equation PEspring = 1/2 k x2
24. Determine GPE and KE for each elevation marked.
60 kg
10 m
GPE = 5880 j
KE = 0
7.5 m
GPE =4410 j
KE = 1470 j
6.0 m
GPE = 3528 j
KE = 2352 j
4.5 m
GPE = 2646 j
KE =3234 j
2.1 m
GPE = 1234.8 j
KE = 4645.2 j
25. A ball bearing rolls along the track below, determine the GPE and KE for each of the labeled
positions. Use the scale 1 mm= 10 cm. The mass of the ball bearing is 0.175 kg. The object is moving
at 1 m/s at point A
A
C
F
D
H
G
B
E
A
GPE = 10.46 j KE = 0.09 j
B
GPE = 4.29 j KE = 6.26 j
C
GPE = 7.72 j
KE = 2.83 j
D
GPE = 5.49 j KE = 5.06 j
E
GPE = 1.03 j
KE = 9.52 j
F
GPE = 6.35 j KE =4.20 j
G
GPE = 4.12 j
KE =6.43 j
H
GPE = 5.49 j KE = 5.06 j
26. A pendulum makes one complete swings from A to B to C and back to A. Describe the energy
transformations that occur during a complete swing. Use the terms maximum, zero, increasing,
or decreasing
A
C
B
at A
GPE = _max____ KE = _0____
A to B
at B
B to C
at C
C to B
GPE = decreasing
GPE = 0
GPE = increasing
GPE =
max
GPE = decreasing
B to A
GPE = increasing KE = decreasing
KE = increasing
KE = max
KE = decreasing
KE = 0
KE = increasing
Kinetic Energy
27. Kinetic energy is the energy of motion.
28. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy
29. There are many forms of kinetic energy. Give 3 examples: vibrational kinetic energy,
rotational kinetic energy, and translational kinetic energy
30. Translational kinetic energy is the name given to energy due to motion from one
location to another.
31. The equation for calculating kinetic energy is 1/2 m v2
32. If we were to increase the speed of an object by three times, the amount of kinetic
energy would increase by nine times.
33. Kinetic energy is a scalar quantity; it does not have a direction. (true, false)
33. Like work and potential energy, the standard metric unit of measurement for
kinetic energy is joule
Mechanical Energy
34. In all instances in which work is done, there is an object which supplies the force
in order to do the work. (true, false)
35. When work is done upon an object, that object gains energy. The energy acquired
by the objects upon which work is done is known as mechanical energy.
36. There are two types of mechanical energy:
potential energy
kinetic energy and
37. Mechanical energy is the energy which is possessed by an object due to its motion
or due to its position.
38. An object which possesses mechanical energy is able to do work
39. A moving car possesses mechanical energy because of its motion (kinetic energy)
40. A moving baseball possesses mechanical energy because of its motion (kinetic energy)
and because of its vertical position above the ground (gravitational potential energy)
41. A barbell lifted above a weightlifter’s head possesses mechanical energy because of its
vertical position above the ground (gravitational potential energy)