Eastern Illinois University

Doug Davis

DDavis@eiu.edu

217.581.6346

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:

1. Momentum has been described as “quantity of motion”; its definition is

a) (

b) m v

d) (

2. A moving object on which no forces are acting will continue to move with constant

a) acceleration

b) impulse

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

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

p =mv

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

5m/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** (

momentumis avectorsodirections are importantP

_{tot,i}= m_{1}v_{1i}+ m_{2}v_{2i}= (m_{1}+ m_{2}) v_{f}= P_{tot,f}m

_{1}v_{1i}+ m_{2}v_{2i}= (m_{1}+ m_{2}) v_{f}(1 kg)(3 m/s) + (2 kg)( - 1 m/s) = (3 kg) v

_{f}(3 - 2) kg m/s = (3 kg) v

_{f}1 kg m/s = 3 kg v

_{f}(1/3) m/s = v

_{f}v

_{f}= 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** (

momentumis avectorsodirections are importantP

_{tot,i}= m_{1}v_{1i}+ m_{2}v_{2i}= (m_{1}+ m_{2}) v_{f}= P_{tot,f}m

_{1}v_{1i}+ m_{2}v_{2i}= (m_{1}+ m_{2}) v_{f}(1 kg)(3 m/s) + (2 kg)( - 2 m/s) = (3 kg) v

_{f}(3 - 4) kg m/s = (3 kg) v

_{f}- 1 kg m/s = 3 kg v

_{f}( - 1/3) m/s = v

_{f}v

_{f}= - 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

a) less than

c) greater than

their total momentum before the collision.

9. When two objects collide and

a) totally elastic 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

c) angular velocity, w

d) work, W

11. Work involves

a) mass multiplied by acceleration

b) mass 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

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

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 v^{2}

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 v^{2}

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**

c) spread out evenly

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 asmallerrotational 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

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

37. If the

a) increase

c) stay the same

38. If Earth's mass

a) decrease to one-ninth 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

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

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

a) v_{1f} = - 1.0 m/s and v_{2f} = 2.0 m/s

b) v_{1f} = 1.0 m/s and v_{2f} = - 2.0 m/s

c) v_{1f} = 1.5 m/s and v_{2f} = 1.5 m/s (*ie,*
v_{if} = v_{2f} = v_{f} = 1.5 m/s)

**d) v _{1f} = 1.0 m/s and
v_{2f} = 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.

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

a) force radially outward.

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}/_{r}2 **.

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.

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.

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

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.

d) weight.