Ex2Sp03

Excursions in Physics
Second Hour Exam
March 5, 2003

For every question, also consider as a possible answer

E) none of the above

1. Which of the following has the largest momentum relative to the earth?
A) a tightrope walker crossing Niagara Falls.
B) a sports car speeding along a highway.
C) a cement truck sitting still in a parking lot.
D) the Science building on campus.

2. A moving object on which the net force is zero will continue to move with constant
A) kinetic energy
B) velocity
C) momentum
D) all of these

3. Impulse is equal to change in
A) kinetic energy
B) momentum
C) potential energy
D) force

4. 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

5. 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) momentum of the rifle is smaller.
D) bullet has less mass than the rifle.

6. 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

7. A 4 kg ball has a momentum of 16 kg m/s. What is the ball's speed?
A) 3 m/s
B) 4 m/s
C) 12 m/s
D) 48 m/s

8. A ball is moving at 6 m/s and has a momentum of 48 kg m/s. What is the ball's mass?
A) 4 kg
B) 8 kg
C) 12 kg
D) 192 kg

9. Exert 3 N for a distance of 3 m in 3 s and you deliver a power of
A) 0.5 W
B) 1.0 W
C) 2.0 W
D) 3.0 W

10. Exert 200 J in 50 s and your power output is
A) 0.5 W
B) 1.0 W
C) 2.0 W
D) 4.0 W

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

12. An object that has potential energy may have this energy because of its
A) speed
B) acceleration
C) momentum
D) position

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

15. For which position above does the ball on the end of the string have the greatest kinetic energy?
D) position D

16. A 3 kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground?
A) 8 J
B) 40 J
C) 80 J
D) 120 J; PE = mgh; PE = (3 kg)(4 m)(10 m/s/s); PE = (3)(4)(10) J; PE = 120 J

17. One car moves 3 times as fast as another identical car. Compared to the slower car, the faster car has
A) the same kinetic energy
B) 3 times the kinetic energy
C) 9 times the kinetic energy; KE = (1/2) m v²
D) 27 times the kinetic energy

18. 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

19. 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) momentum
B) kinetic energy
C) velocity
D) all of the above

20. What does an object have when moving that it doesn`t have when at rest?
A) momentum
B) energy
C) mass
D) all of the above

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

22. Horses that move with the fastest linear speed on a merry-go-round are located
A) nearer to the center
B) nearer to the edge
C) always white (I like this one!)
D) in front of the slower ones

23. An industrial flywheel has a greater rotational inertia when most of its mass is
A) nearer the axis
B) nearer the rim
C) spread out evenly

24. 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 a smaller moment of intertia, so it is easier to rotate.
B) ring
C) neither; they both reach the bottom at the same time

25. When a twirling ice skater extends her arms outward, her rotational speed
A) increases
B) decreases; Since her angular momentum is conserved, and increase in rotational mass requires a decrease in rotational speed.
C) remains the same (or is conserved)

26. Kepler’s Laws of Planetary Motion were “discovered” or produced by Johannes Kepler, using a lifetime of observational data taken by
A) Nicholas Copernicus
B) Galileo
C) Tycho Brahe
D) Isaac Newton

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

28. According to Kepler’s Laws of Planetary Motion, as a planet gets closer to the Sun,
A) it becomes warmer.
B) its speed increases.
C) its period increases.
D) its mass decreases.

29. 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

30. 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

31. What is the force of gravity on a 80-kg man standing on Earth's surface?
A) 9.8 N
B) 80 N
C) 800 N; w = m g; w = (80 kg)(10 m/s/s); w = (80)(10) N
D) 8,000 N

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

33. If Earth's mass decreased to one-half its original mass with no change in radius, then your weight would
A) decrease to one-quarter its original value
B) decrease to one-half its original value
C) remain the same
D) increase to twice its original value

34. The force of gravity acting on the Space Shuttle in orbit is nearly
A) zero because it is weightless
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 percent of its weight at Earth’s surface

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

36 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; their distances from the center of Earth are all practically the same.
D) twice the weight

37. 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.
C) Jupiter's radius is 10 times Earth's radius.
D) you are 100 times more weightless there.

38. The period for the Space Shuttle, or any other satellite in a low-Earth orbit, is about
a) 17 minutes.
b) an hour and a half.
c) 24 hours.
d) 28 days.

39. Communications satellites are often placed in geosynchronous orbits. The radius of a geosynchronous orbit is about
a) 500 to 600 km
b) 17,000 km
c) 42,000 km
d) 450,000 km

40. 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.
c) zero because its speed remains constant.
d) directed outward, away from the center of the curve.

41. The moon travels in a nearly circular orbit at a nearly constant speed.
a) The acceleration of gravity on the moon’s surface is about one-sixth the value at Earth’s surface.
b) The force of gravity between Earth and the moon provides the centripetal force necessary to keep the moon in its orbit.
c) The force of gravity causes the moon to “fall” one-twentieth of an inch each second toward Earth when compared to the straight line path it would take if gravity were suddenly turned “off”.
d) all of the above.

42. Projectile motion is a combination of
a) horizontal motion with constant, non-zero acceleration and vertical motion with constant velocity
b) horizontal motion with constant non-zero acceleration and vertical motion with constant, non-zero acceleration
c) horizontal motion with constant velocity and vertical motion with constant, non-zero acceleration
d) horizontal motion with constant velocity and vertical motion with constant velocity

43. When a ball or stone or other object is thrown or hit or fired, and air resistance can be neglected, the resulting motion is known as projectile motion. The path of an object in projectile motion is
a) a quadrant of a circle
b) a hyperbola
c) a parabola
d) a straight line

44. Consider a ball thrown horizontally from the edge of a balcony with an initial velocity of 20 m/s. The ball is thrown from 5 m above the ground. How long is it in the air? That is, when does it strike the ground?
a) 0.5 s
b) 1.0 s

y = (1/2) g t²
5 m = (1/2) (10 m/s/s)(t²)
1 s²= t²
t = 1 s

c) 1.5 s
d) 2.0 s

45. Consider a ball that is thrown horizontally from the edge of a building with an initial velocity of 20 m/s. The ball is thrown from 5 m above the ground. How far from the building does the ball strike the ground?
a) 5 m
b) 10 m
c) 15 m
d) 20 m ; x = v_x t; x = (20 m/s)(1 s); x = 20 m

46. Consider a ball thrown from a level surface with an initial upward velocity of 20 m/s and an initial horizontal velocity of 5 m/s. How long is the ball in the air?
a) 0.5 s
b) 1.0 s
c) 2.0 s
d) 4.0 s

When the ball returns to the level surface, v_y = - v_iy = - 20 m/s

v_y = v_iy + a_y t

v_y = 20 m/s + ( - 10 m/s/s) t

- 20 m/s = 20 m/s - (10 m/s/s) t

- 40 m/s = - (10 m/s/s) t

4 s = t

47. Consider a ball thrown from a level surface with an initial upward velocity of 20 m/s and an initial horizontal velocity of 5 m/s. Where does it land? That is, measured from its initial position, where does it come back to and strike the level surface?
a) 5 m
b) 10 m
c) 15 m
d) 20 m

x = v_x t

x = (5 m/s)(4 s)

x = 20 m

48. A golf ball is given a velocity of 8 m/s horizontally and 15 m/s vertically. How long is it in the air, before coming back to its initial vertical height? That is, how long is it in the air before striking the level ground?
a) 1.5 s
b) 2.0 s
c) 3.0 s

As before, we can set v_y = - v_iy

v_y = - 15 m/s

v_y = v_iy + a_y t

v_y = 15 m/s + ( - 10 m/s/s) t

- 15 m/s = 15 m/s + ( - 10 m/s/s) t

- 30 m/s = - (10 m/s/s) t

3 s = t

d) 4.0 s

49. A golf ball is given a velocity of 8 m/s horizontally and 15 m/s vertically. How far, horizontally, does it travel before coming back to its initial vertical height? That is, where does it hit the level ground?
a) 8 m
b) 12 m
c) 24 m; x = v_x t; x = (8 m/s)(3 s); x = 24 m
d) 48 m

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

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