Eastern Illinois University
Doug Davis
DDavis@eiu.edu
217.581.6346

PHY 3050G
Excursions in Physics

Second Hour Exam
February 26, 2001

Enter all your answers in the "scantron sheet" or the "bubble sheet". Turn in only that sheet. Anything you write on this exam will not be seen or used or considered or graded. Be sure your name is on the "bubble sheet" you hand in. Be sure your name is bubbled-in. Be sure your answers are recorded correctly.

Possibly useful information:

For every question, also consider the following as a possible answer:
e) none of the above

For every question, also consider the following as a possible answer:
e) none of the above

1. Momentum has been described as “quantity of motion”; its definition is
a) (1/2) m v2
b) m v2
c) m v
d) (1/) m v

2. A moving object on which no forces are acting will continue to move with constant
a) acceleration
b) impulse
c) momentum Since p = m v, constant velocity also means constant momentum.
d) all of these

3. 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; F12 = - F21
d) International shortages of momentum

4. A 6 kg ball has a momentum of 30 kg m/s. What is the ball's speed?
a) 2.5 m/s
b) 5.0 m/s

p = m v

30 kg m/s = (6 kg) ( v )

5 m/s = v

c) 12.5 m/s
d) 180 m/s

5. A 1-kg cart, initially moving to the right at 3.0 m/s, strikes a 2-kg cart, initially moving to the left at 1.0 m/s. The two c collide inelastically (ie, they stick together). What is their common final velocity?
a) 0.33 m/s.

momentum is a vector so directions are important

Ptot,i = m1 v1i + m2 v2i = (m1 + m2 ) vf = Ptot,f

m1 v1i + m2 v2i = (m1 + m2 ) vf

(1 kg)(3 m/s) + (2 kg)( - 1 m/s) = (3 kg) vf

(3 - 2) kg m/s = (3 kg) vf

1 kg m/s = 3 kg vf

(1/3) m/s = vf

vf = 0.33 m/s

b) 0.67 m/s.
c) 1.33 m/s.

d) 2.0 m/s.

6. A 1-kg cart, initially moving to the right at 3.0 m/s, strikes a 2-kg cart, initially moving to the left at 2.0 m/s. The two c collide inelastically (ie, they stick together). What is their common final velocity?
a) - 0.33 m/s (ie, to the left).

momentum is a vector so directions are important

Ptot,i = m1 v1i + m2 v2i = (m1 + m2 ) vf = Ptot,f

m1 v1i + m2 v2i = (m1 + m2 ) vf

(1 kg)(3 m/s) + (2 kg)( - 2 m/s) = (3 kg) vf

(3 - 4) kg m/s = (3 kg) vf

- 1 kg m/s = 3 kg vf

( - 1/3) m/s = vf

vf = - 0.33 m/s

b) - 0.67 m/s (ie, to the left).
c) 0.33 m/s (ie, to the right).
d) 1.33 m/s (ie, to the right).

7. If two objects collide and do not stick together, their total momentum after the collision is
a) less than
b) the same as
c) greater than
their total momentum before the collision.

8. If two objects collide and stick together, their total momentum after the collision is
a) less than
b) the same as
c) greater than
their total momentum before the collision.

9. When two objects collide and stick together, this type of collision is known as a
a) totally elastic collision.
b) totally inelastic collision.
c) totally natural collision.
d) totally impulsive collision.

10. In a “totally elastic collision” another quantity -- in addition to momentum -- is also conserved. That other conserved quantity is the
a) velocity, v
b) kinetic energy, KE
c) angular velocity, w
d) work, W

11. Work involves
a) mass multiplied by acceleration
b) mass multiplied by distance
c) force multiplied by distance
d) force multiplied by time

12. 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.

13. 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.

14. Exert 6 N for a distance of 5 m in 3 s and you deliver a power of
a) 2.5 W
b) 6.0 W
c) 8.0 W
d) 10.0 W

P = W / t

P = [(6 N)(5 m)] / 3 s

P = 30 Nm / 3 s

P = 30 J / 3 s

P = 10 J/s

P = 10 W

15. An object is raised above the ground gaining a certain amount of potential energy. If the same object is raised twice as high it gains
a) half as much energy
b) the same amount of energy
c) twice as much energy

PE = m g h

d) four times as much energy

16. An object that has kinetic energy must be
a) elevated
b) falling
c) moving

KE = (1/2) m v2

d) at rest

17. An object that has potential energy may have this energy because of its
a) speed
b) acceleration
c) momentum
d) position

18. 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

19. For which position above does the ball on the end of the string have the greatest gravitational potential energy?

a) Position A

PE = m g h

h is greatest for postion A

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

d) Position D

PE = m g h

h is smallest for position D

That means PE(D) is smallest

But KE + PE = constant

Therefore KE is greatest at position D

21. A 10 kg sack is lifted 4 meters in the same time as a 5 kg sack is lifted 2 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
c) twice as much
d) four times as much

22. A 3 kg mass is held 5 m above the ground. What is the approximate potential energy of the mass with respect to the ground?
a) 15 J
b) 75 J
c) 150 J
d) 300 J

23. A 10 kg mass has 50 J of potential energy with respect to the ground. Approximately how far is it located above the ground?
a) 0.5 m
b) 1 m
c) 5 m
d) 10 m

24. A 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

25. A car moving at 40 km/hr skids 20 m with locked brakes. How far will the car skid with locked brakes if it is traveling at 120 km/hr?
a) 60 m
b) 90 m
c) 180 m
d) 540 m

26. 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

27. If an object has kinetic energy, then it also must have
a) momentum
b) velocity
c) speed
d) all of the above

28. Consider a diver who does a somersault off a high dive. While doing the somersault, he pulls himself into a tuck position. Just before he enters into the water, he stretches himself out full length. This causes him to slow his rotation because of
a) air resistance to his now extended body.
b) conservation of energy.
c) conservation of angular velocity.
d) conservation of angular momentum.

29. Consider a diver who does a somersault off a high dive. While doing the somersault, he pulls himself into a tuck position. Just before he enters into the water, he stretches himself out full length. This causes him to slow his rotation because
a) his body now has a much larger air resistance.
b) his body now has a much larger moment of inertia.

Angular momentum is conserved.

Angular momentum = (moment of inertia) x (rotational velocity)

Making the moment of inertia larger causes the rotational velocity to be smaller.

(moment of inertia) x (rotational velocity) =

= (moment of inertia) x (rotational velocity)

c) his gravitational potential is now greater.
d) his angular momentum is now greater.

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

31. A hollow ring or hoop and a solid cylinder roll down an incline starting at the same time. The one to reach the bottom first will be the
a) cylinder

The solid cylinder has a smaller rotational mass (or moment of inertia)

so it is easier to rotate.

b) hoop or ring
c) neither; they both reach the bottom at the same time

32. 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 factor of
a) two
b) four
c) eight
d) sixteen

Question 32 was wrong on my answer key; I have changed your score in my records.

33. When a twirling ice skater extends her arms outward, her rotational speed
a) increases
b) decreases
c) remains the same (ie, it is conserved).

34. According to Kepler's laws, the paths of planets about the Sun are
a) straight lines
b) parabolas
c) ellipses
d) hyperbolas

35. 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

36. 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

37. If the mass of Earth somehow decreased with no change in radius, your weight would
a) increase
b) decrease
c) stay the same

38. If Earth's mass decreased to one-third its original mass with no change in radius, then your weight would
a) decrease to one-ninth its original value
b) decrease to one-third its original value
c) increase to nine times its original value
d) increase to three times its original value

39. 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

40. 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

41. 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.
d) you are 100 times more weightless there.

42. A 3.0-kg cart, initially moving to the right at v1i = 2.0 m/s, collides with a 1.0-kg cart, initially at rest (v2i = 0). The collision is totally elastic. After the collision, the carts have final velocities of

a) v1f = - 1.0 m/s and v2f = 2.0 m/s
b) v1f = 1.0 m/s and v2f = - 2.0 m/s
c) v1f = 1.5 m/s and v2f = 1.5 m/s (ie, vif = v2f = vf = 1.5 m/s)
d) v1f = 1.0 m/s and v2f = 3.0 m/s

43. 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 is known as the centripetal force.

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

44. A communications satellite appears stationary to an Earth-based observer. The orbit such a satellite is in is called a
a) low-Earth orbit.
b) polar orbit.
c) geosynchronous orbit.
d) high-Earth orbit.

45. A satellite is held in orbit by the force of gravity. This force of gravity provides a
b) boost or force along the direction of motion.
c) centripetal force.
d) geosynchronous node for communications satellites.

46. Gravity is one of the four fundamental forces. Its range is
a) very short.
b) infinite; it varies as 1/r .
c) infinite; it varies as 1/r2 .
d) limited to just slightly more that the diameter of our solar system

47. If you listen to a TV interview with someone on the other side of the world where the signal is sent via a communications satellite, you will notice a delay from the time a question is asked until the reply is started. This is because
a) electronics used in such satellites use slow circuits to conserve power.
b) people want to be careful that they have understood the question.
c) such satellites are so high that it takes about a second for electromagnetic waves to travel to the satellite and back.
d) television news producers want at least a brief amount of time in case they need to censor a reply.

48. If we could, somehow, turn off gravity, our Moon would
a) slowly spiral away from Earth.
b) move off in a straight line, tangent to its orbit.
c) move away along a radial path.
d) slowly spiral toward Earth until it crashed into it.

49. As your kinetic energy is reduced to zero in an automobile crash, use of seat belts means a stopping force is applied to your body over a greater distance. This means the force on you is
a) less than
b) the same as
c) more than
if you were not wearing seat belts.

50. As you climb the first hill of a roller coaster, work is done by outside forces. At the top of that first hill, your velocity is nearly zero and you have maximum
a) momentum.
b) kinetic energy.
c) potential energy.
d) weight.