PHY 3050 G
Excursions in Physics
Second Hour Exam
October 16, 2002

For every question, also consider as a possible answer
E) none of the above

1. Conservation of momentum is directly related to
A) Newton’s First Law of Motion
B) Newton’s Second Law of Motion
C) Newton’s Third Law of Motion
D) International shortages of momentum

2. A rifle recoils from firing a bullet. The speed of the rifle's recoil is small because the
A) force against the rifle is smaller than against the bullet.
B) momentum is mainly concentrated in the bullet.
C) rifle has more mass than the bullet.
D) momentum of the rifle is smaller.

3. Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a greater
A) speed
B) acceleration
C) momentum
D) all of the above

4. A car traveling along the highway needs a certain amount of force exerted on it to stop. More stopping force may be required when the car has
A) mass
B) momentum
C) less stopping distance
D) all of the above

5. A 2 kg ball has a momentum of 12 kg m/s. What is the ball's speed?
A) 3 m/s
B) 4 m/s
C) 6 m/s
p = m v
12 kg m/s = (2 kg) (v)
12 kg m/s = (2 kg)(6 m/s)

D) 12 m/s

6. A ball is moving at 8 m/s and has a momentum of 24 kg m/s. What is the ball's mass?
A) 3 kg
p = m v
24 kg m/s = (m)(8 m/s)
24 kg m/s = (3 kg)(8 m/s)

B) 4 kg
C) 6 kg
D) 192 kg

7. If you push an object twice as far while applying the same force you do
A) half as much work
B) the same amount of work
C) twice as much work
D) four times as much work

8. If you push an object just as far while applying twice the force you do
A) half as much work
B) the same amount of work
C) twice as much work
D) four times as much work

9. Exert 2 N for a distance of 2 m in 2 s and you deliver a power of
A) 0.5 W
B) 1.0 W
C) 2.0 W
P = Work/time
P = [(2 N)(2 m)]/2 s
P = 4 J/2 s
P = 2 W

D) 3.0 W

10. Exert 100 J in 50 s and your power output is
A) 0.5 W
B) 1.0 W
C) 2.0 W
P = 100 J/50 s
P = 2 W

D) 4.0 W

11. An object that has kinetic energy must be
A) elevated
B) falling
C) moving
D) at rest

12. A person can lift containers a vertical distance of 1 meter or can roll them up a 4 meter-long ramp to the same elevation. With the ramp, the applied force required is about
A) one-fourth as much
B) half as much
C) the same
D) four times as much

13. When a car is braked to a stop, its kinetic energy is transformed to
A) energy of motion
B) heat energy
C) stopping energy
D) potential energy

14. For which position above does the ball on the end of the string have the greatest gravitational potential energy?
A) position A
PEg = m g h

15. For which position above does the ball on the end of the string have the greatest kinetic energy?
D) position D
At position D, the PEg is minimal so KE is maximum.

16. Which requires more work: lifting a 5 kg sack vertically 2 meters or lifting a 10 kg sack vertically 4 meters?
A) lifting the 5 kg sack
B) both require the same amount of work
C) lifting the 10 kg sack
W = m g h
W10 = (10 kg)(10 m/s2) (4 m) = 400 J
W5 = (5 kg)(10 m/s2) (2 m) = 100 J

D) both require the same amount of force

17. A 10 kg sack is lifted 2 meters in the same time as a 5 kg sack is lifted 4 meters. The power expended in raising the 10 kg sack compared to the power used to lift the 5 kg sack is
A) half as much
B) the same
W = m g h
W10 = (10 kg)(10 m/s2) (2 m) = 200 J
W5 = (5 kg)(10 m/s2) (4 m) = 200 J
Power = Work/time
Since the times are the same and work is the same for both,
the power is the same for both.

C) twice as much
D) four times as much

18. A 2 kg mass has 40 J of potential energy with respect to the ground. Approximately how far is it located above the ground?
A) 1 m
B) 2 m
PEg = m g h
40 J = (2 kg) (10 m/s2) (h)
40 J = (2 kg) (10 m/s2) (2 m)

C) 3 m
D) 4 m

19. Using 1,000 J of work, a model elevator is raised from the ground floor to the second floor in 20 seconds. How much power does the elevator use?
A) 50 W
P = W/t
P = 1000 J/20 s
P = 50 W

B) 500 W
C) 2 kW
D) 20 kW

20. A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has
A) the same kinetic energy
B) 4 times the kinetic energy
C) 8 times the kinetic energy
D) 16 times the kinetic energy
KE = (1/2) m v2

21. A car moving at 50 km/hr skids 20 m with locked brakes. How far will the car skid with locked brakes if it is traveling at 150 km/hr?
A) 40 m
B) 60 m
C) 90 m
D) 180 m
KE = (1/2) m v2
Remember, KE goes like v-squared!
That means, increasing v by a factor of three
increases the KE
by a factor of nine!

22. When a rifle is fired it recoils so both the bullet and rifle are set in motion. The rifle and bullet ideally acquire equal but opposite amounts of
A) kinetic energy
B) momentum
C) potential energy
D) all of the above

23. If an object has kinetic energy, then it also must have
A) momentum
B) velocity
C) speed
D) all of the above

24. In the colliding balls apparatus, sometimes known as "Newton’s Pendulums", if one ball is dropped into the line of balls and a single ball came out the other side with twice the speed,
A) kinetic energy would be conserved but momentum would not.
B) kinetic energy would be conserved but potential energy would not.
C) momentum would be conserved but kinetic energy would not.
This is homework problem Ex 6.23.

D) potential energy would be conserved but momentum would not.

25. According to Kepler's laws, the paths of planets about the Sun are
A) straight lines
B) parabolas
C) ellipses
D) hyperbolas

26. According to Kepler’s laws, a planet
A) speeds up as it gets farther from the Sun.
B) speeds up as it gets close to the Sun.
Equal areas are swept out in equal times.

C) moves in circles which move around other circles.
D) must have at least one moon.

27. According to Newton, the greater the masses of interacting objects, the
A) greater the force of gravity, by the product of the masses
B) less the force of gravity
C) greater the force of gravity, by the square of the masses
D) less the force of gravity, inversely as the square of the masses

28. According to Newton, the greater the distance between masses of interacting objects, the
A) greater the force of gravity, proportional to the distance
B) less the force of gravity, inversely as the distance
C) greater the force of gravity, proportional to the square of the distance
D) less the force of gravity, inversely as the square of the distance

29. What is the force of gravity on a 500-newton woman standing on the earth's surface?
A) 9.8 N
B) 50 N
C) 500 N
D) 5,000 N

30. A woman who normally weighs 400 N stands on top of a very tall ladder so she is one earth radius above the earth's surface. How much would she weigh there?
A) zero
B) 100 N
C) 200 N
D) 400 N

31. If the mass of the earth somehow increased with no change in radius, your weight would
A) increase
B) decrease
C) stay the same

32. If the radius of Earth somehow decreased with no change in mass, your weight would
A) increase
B) decrease
C) stay the same

33. The force of gravity acting on the Space Shuttle in orbit is nearly
A) zero
B) equal to the weight of the Space Shuttle at Earth’s surface
C) about one-tenth its weight at Earth’s surface
D) about one-one hundredth its weight at Earth’s surface

34. The force of gravity acts on all apples on an apple tree. Some apples are twice as far from the ground as others. These twice-as-high apples, for the same mass, have practically
A) one-fourth the weight
B) one-half the weight
C) the same weight
D) twice the weight

35. The planet Jupiter is about 300 times as massive as Earth, yet on its surface you would weigh only about 3 times as much. This is because
A) your mass is 100 times less on Jupiter.
B) Jupiter is significantly farther from the sun.
This is homework problem Ex 8.15.

D) you are 100 times more weightless there.

36. An industrial flywheel has a greater rotational inertia when most of its mass is
A) nearer the axis
B) nearer the rim

37. A cylinder and a ring roll down an incline starting at the same time. The one to reach the bottom first will be the
A) cylinder
The cylinder has a smaller “rotational mass” or
moment of inertia so it is easier to rotate so
it reaches the bottom firs.

B) ring
C) neither; they both reach the bottom at the same time

38. Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you'll increase the torque by
A) two
B) four
C) eight
D) sixteen

39. When a twirling ice skater brings her arms inward, her rotational speed
A) increases
B) decreases
C) remains the same (or is conserved)

40. To turn a stubborn screw, it is best to use a screwdriver that has a handle that is
A) long and thin
B) thick or wide
C) yellow
D) slippery

41. To pry open a lid from a can of paint, it is best to use a screwdriver that has a handle that is
A) long and thin
B) thick or wide
C) yellow
D) slippery

42. A car travels in a circle with constant speed. The net force on the car is
A) directed forward, in the direction of travel.
B) directed towards the center of the curve.
This net force may called the “centripetal force”.

C) zero because the car is not accelerating.
D) directed outward, away from the center of the curve

43. Henry Cavendish devised an extremely sensitive instrument to measure the very small gravitational force between two ordinary sized masses. This allowed him to measure big "G" in Newton’s Law of Universal Gravitation. This instrument is known as a
A) Cavendish G-meter
B) Newtonian pendulum
C) Cavendish balance
D) Newtonian revlector

44. Henry Cavendish measured big "G" in Newton’s Law of Universal Gravitation. He presented his findings in London at a meeting of the Royal Society. His paper was entitled
A) Tripping the Light.
B) Weighing the Earth.
C) Measuring big "G" in Newton’s Law of Universal Gravitation.
D) A Lever for London.

45. In measuring big "G" in Newon’s Law of Universal Gravitation, Henry Cavendish used an "optical lever". An optical lever is used to measure
A) wavelengths of light
B) optical torques
C) very small changes in angle
D) very large changes in speed

46. A geo-synchronous communications satellite is in
A) a polar orbit
B) a low-earth orbit
C) an equatorial orbit
D) apogee

47. The Space Shuttle usually goes in
A) a polar orbit
B) a low-earth orbit
C) an equatorial orbit
D) apogee

48. The Space Shuttle has an orbital speed of about
A) 6,000 km/h
B) 28,000 km/h
C) 42,000 km/h
D) 428,000 km/h

49. The Space Shuttle has a period of about
A) 125 seconds
B) 90 minutes
C) 24 hours
D) 27.3 days

50. A geo-synchronous communications satellite has a period of about
A) 125 seconds
B) 90 minutes
C) 24 hours
D) 27.3 days