Physics 2017-1018

Unit 5 Practice Name __________________________________

1. Work may be expressed using all of the following units except:

Nm 2 kg m 2
A) ! B) joule C) ! D) watt second E) kilowatt hour
kg 2 s2

2. A concrete block is pulled 7.0 m across a frictionless surface by means of a rope. The tension in the
rope is 40 N; and the net work done on the block is 247 J. What angle does the rope
make with the horizontal? θ

A) 47°
B) 62°
C) 28°
D) 41°
E) 88°
3. A 5.00-kg block of ice is sliding across a frozen pond at 2.00 m/s. A 7.60-N force is applied in the direction of motion.
The ice block slides 15.0 m; and then the force is removed. The work done by the applied force is
A) +735 J
B) +114 J
C) +19.7 J
D) –735 J
E) –114 J
4. A force of magnitude 25 N directed at an angle of 37° above the horizontal moves a 10-kg crate along a horizontal
surface at constant velocity. How much work is done by this force in moving the crate a distance of 15 m?
A) 98 J
B) 300 J
C) 40 J
D) 1.7 J
E) zero
5. A 1.0-kg ball on the end of a string is whirled at a constant speed of 2.0 m/s in a horizontal circle of radius 1.5 m. What
is the work done by the centripetal force during one revolution?
A) 25 J
B) 33 J
C) 6.0 J
D) 2.7 J
E) zero
6. Which one of the following statements concerning kinetic energy is true?
A) It is a quantitative measure of inertia.
B) It is directly proportional to velocity.
C) It is always equal to the potential energy.
D) It is never negative.
E) It can be measured in watts.
7. Which one of the following has the largest kinetic energy?
A) the space shuttle orbiting the Earth
B) a woman swimming
C) the earth moving in its orbit around the sun
D) a jet airplane flying at maximum speed
E) a raindrop falling
8. In which one of the following situations will there be an increase in kinetic energy?
A) A stone at the end of a string is whirled in a horizontal circle at constant speed.
B) A projectile approaches its maximum height.
C) A box is pulled across a rough floor at constant speed.
D) A satellite travels in a circular orbit around the earth at fixed altitude.
E) A child pushes a merry go round causing it to rotate faster.
9. A 1500-kg car travels at a constant speed of 22 m/s around a circular track which is 80 m across. What is the kinetic
energy of the car?

A) ! 7.2 × 105 J B) zero C) ! 3.3× 104 J D) ! 1.6 × 104 J E) ! 3.6 × 105 J

10. A car with kinetic energy ! 8 × 106J travels along a horizontal road. How much work is required to stop the car in 10 s?

A) ! 8 × 105 J B) ! 8 × 104 J C) zero D) ! 8 × 107 J E) ! 8 × 106 J

11. How much energy is dissipated in braking a 1,000-kg car to a stop from an initial speed of 20 m/s?
A) 800,000 J B) 10,000 J C) 20,000 J D) 200,000 J E) 400,000 J
12. A 10.0-g bullet traveling horizontally at 755 m/s strikes a stationary target and stops after penetrating 14.5 cm into the
target. What is the average force of the target on the bullet?

A) ! 3.13× 104 N B) ! 2.07 × 105 N C) ! 3.93× 104 N D) ! 6.26 × 103 N E) ! 1.97 × 104 N

13. Use-energy principles to find the force required to accelerate an electron (! m = 9.11× 10−31 kg ) from rest to a speed of

! 1.5 × 107 m/s in a distance of 0.0125 m.

A) ! 3.56 × 10−19 N
B) ! 8.20 × 10−17 N
C) ! 8.20 × 10−15 N
D) ! 1.64 × 10−14 N
E) ! 5.47 × 10−22 N

14. In which one of the following systems is there a decrease in gravitational potential energy?
A) a crate rests at the bottom of an inclined plane
B) water is forced upward through a pipe
C) a girl jumps down from a bed
D) a boy stretches a horizontal spring
E) a car ascends a steep hill
15. A 40-kg block is lifted vertically 20 meters from the surface of the earth. To one significant figure, what is the change in
the gravitational potential energy of the block?
A) –800 J B) +8,000 J C) –8,000 J D) +800 J E) zero
16. A 12-kg crate is pushed up an incline from point A to point B
B as shown in the figure. What is the change in the • 7.5 m
gravitational potential energy of the crate? A
A) +1200 J • 2.5 m
B) +60 J
C) –1200 J
D) +590 J
E) –590 J
17. A woman stands on the edge of a cliff and throws a stone vertically downward with an initial speed of 10 m/s. The
instant before the stone hits the ground below, it has 450 J of kinetic energy. If she were to throw the stone horizontally
outward from the cliff with the same initial speed of 10 m/s, how much kinetic energy would it have just before it hits the
ground?
A) 950 J B) 800 J C) 50 J D) 450 J E) 100 J
18. A block is dropped from a high tower and is falling freely under the influence of gravity. Which one of the following
statements is true concerning this situation? Neglect air resistance.
A) The kinetic energy increases by equal amounts over equal distances.
B) As the block falls, the net work done by all of the forces acting on the block is zero.
C) The total energy of the block increases by equal amounts over equal distances.
D) The potential energy of the block decreases by equal amounts in equal times.
E) The kinetic energy of the block increases by equal amounts in equal times.
19. Two boxes are connected to each other as shown. The system is released from rest and 3 kg
the 1.00-kg box falls through a distance of 1.00 m. The surface of the table is
frictionless. What is the kinetic energy of box B just before it reaches A
the floor?
A) 39.2 J B 1 kg
B) 29.4 J
C) 9.80 J 1m
D) 4.90 J
E) 2.45 J

vi = 1.5 m/s
0.5 kg

1.9 m
1.8 m
r = 0.9 m

3. Designers are working on a new roller-coaster, and they begin by making a scale model. On this model, a car of total
mass 0.5 kg moves with negligible friction along a track shown in the figure above. The car is given an initial speed
! vi = 1.5 m/s at the top of the first hill of height 1.9 m. Point A is located at a height of 1.8 m at the top of the second hill, the
upper part of which is a circular arc of radius 0.9 m.
A) Calculate the speed of the car at point A.
B) In order to stop the car at point A, some friction must be introduced. Calculate the work that must be done by the
frictional force in order to stop the car at point A.
C) Explain how to modify the track so that with the same initial speed, the car will just lose contact with the track at
point A before descending down the track. Calculate exactly how to modify the track.
Two hands push horizontally on a block as shown below on the right. Hand 1 pushes to the right, and hand 2 pushes to the
left. We choose to let the positive direction be to the right. Let ! WH represent the work done by hand 1, and ! WH the
1 2
work done by hand 2.
A) Complete the table below by filling in the signs of the quantities listed for the given situations. If a quantity is zero,
fill in a zero for the sign.
Sign of Sign of Sign of
Sign of Sign of
! Δr ΣF W H 1
W H W H + WH
2 1 2

Speeds up
Moves +
Slows down
right H1 H2
Constant speed
Speeds up
Moves Slows down
left
Constant speed
!

A
10 m/s
C
B 37°

20 m
D
!

6. A 60 kg ski jumper starts from rest at point A at the top of a run and leaves the ramp at point B with a speed of 10 m/s at
an angle of 37° to the horizontal. Point B is 20 m above ground level. Ignore friction.
A) What is the height of point A above ground level?

!
B) What is his height above ground level at the peak of his jump (point C)? (Hint: What is his speed at point C?)

!
C) What is his speed when he lands on the ground at point D?

!
D) If the jumper actually lands at point D with a speed of 18 m/s, how much work was done by air friction?