Eastern Illinois University

Doug Davis

DDavis@eiu.edu

217.581.6346

“Excursions Live!”

Second Hour Exam

October 4, 2000

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

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For every question, also consider the following as a possible answer:

**e)** none of the above

1. Which of the following has the largest momentum relative to
Earth?

a) a tightrope walker crossing Niagara Falls.

b) a truck speeding along a highway.P = m vc) a Mack truck sitting in the parking lot. While the

massis large, the velocity iszero.

d) the Science building on campus.While themassis even larger, the velocity is stillzero.

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

a) acceleration

b) impulse

c) momentumF =ma

F = 0meansa = 0

a = 0meansv = const

v = constmeansp =mv=constantd) 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 MotionWe used F_{12}= - F_{21}in developing the idea that the change in the momentum of object ONE was the same but in the opposite direction to the change in momentum of object TWO. That means the TOTAL momentum remains CONSTANT.d) International shortages of momentum

4. A 5 kg ball has a momentum of 30 kg m/s. What is the ball's
speed?

a) 3 m/s

b) 6 m/sP = m v

30 kg m/s = (5 kg) (6 m/s)

v = 6 m/sc) 15 m/s

d) 150 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** (

a) 0.33 m/s.Initially,beforethe collision,

P+_{Tot,i}= m_{1}v_{1i}m_{2}v_{2i}

P_{Tot,i}= ( 1 kg ) ( 3 m/s ) + ( 2 kg ) ( - 1 m/s )

P_{Tot,i}= ( 3 - 2 ) kg m/s

P_{Tot,i}= 1 kg m/s

Finally,afterthe collision,

P_{Tot,f}= ( 3 kg ) ( v_{f})

Conservation of momentum tells us these two valus of thetotalmomentum are thesame,

P_{Tot,f}= ( 3 kg ) ( v_{f}) = 1 kg m/s = P_{Tot,i}

( 3 kg ) ( v_{f}) = 1 kg m/s

v_{f}= [ 1 kg m/s ] / 3 kg

v_{f}= 0.33 m/sb) 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** (

a) - 0.33 m/s (ie,to theleft).Initially,beforethe collision,

P+_{Tot,i}= m_{1}v_{1i}m_{2}v_{2i}

P_{Tot,i}= ( 1 kg ) ( 3 m/s ) + ( 2 kg ) ( - 2 m/s )

P_{Tot,i}= ( 3 - 4 ) kg m/s

P_{Tot,i}= - 1 kg m/s

Finally,afterthe collision,

P_{Tot,f}= ( 3 kg ) ( v_{f})

Conservation of momentum tells us these two valus of thetotalmomentum are thesame,

P_{Tot,f}= ( 3 kg ) ( v_{f}) = - 1 kg m/s = P_{Tot,i}

( 3 kg ) ( v_{f}) = - 1 kg m/s

v_{f}= [ - 1 kg m/s ] / 3 kg

v_{f}= - 0.33 m/sb) - 0.67 m/s (

ie,to theleft).

c) 0.33 m/s (ie,to theright).

d) 1.33 m/s (ie,to theright).

7. If two objects collide and do __not__ stick together, their
total momentum after the collision is

a) less than

b) the same asMomentum isalwaysconserved!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 asMomentum isalwaysconserved!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.Splat!c) totally natural collision.

d) totally impulsive collision.

10. Momentum is conserved in any collision. In a “totally
elastic collision” another quantity is also conserved. That
other conserved quantity is the

a) velocity, v

b) kinetic energy, KEBoing!c) angular velocity, w

d) work, W

11. Work involves

a) mass multiplied by acceleration

b) mass multiplied by distance

c) force multiplied by distanced) 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 4 N for a distance of 5 m in 2 s and you deliver a power
of

a) 2.5 W

b) 6.0 W

c) 8.0 W

d) 10.0 WP = Work / time

P = [ ( 4 N ) ( 5 m ) ] / 2 s

P = [ 20 N-m ] / 2 s

P = 20 J / 2 s

P = 10 W

15. Exert 2,500 J of work in 50 s and your power output is

a) 5 W

b) 10 W

c) 25 W

d) 50 WP = Work / time

P = 2,500 J / 50 s

P = 50 W

16. 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 energyPE_{grav}= m g hd) four times as much energy

17. An object that has **kinetic** energy must be

a) elevated

b) falling

c) movingKE =^{1}/_{2}m v^{2}d) at rest

18. An object that has potential energy may have this energy because
of its

a) speed

b) acceleration

c) momentum

d) positionPEis an example_{grav}= m g h

19. 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

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

a) Position APE_{grav}= m g h

At position A, h is a maximum so the PE is a maximum

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

d) Position DPE_{grav}= m g h

At position D, h is a minimum so the PE is a minimum.

When (or where) PE is a minimum, the KE is a maximum.

22. 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

23. 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

24. 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

25. 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

d) 27 times the kinetic energy

26. 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) 120 m

d) 180 mTraveling with 3 times the velocity means having 9 times the KE so 9 times a much work is req'd to bring it to rest.

27. 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

28. What does an object have when moving that it doesn`t have when at
rest?

a) momentump = m vb) energy

c) mass

d) all of the above

29. If an object has kinetic energy, then it also must have

a) momentum

b) velocity

c) speed

d) all of the above

30. According to Kepler's laws, the paths of planets about the Sun
are

a) straight lines

b) parabolas Parabolas are the paths taken withprojectile motion.

c) ellipses

d) hyperbolas

31. According to Newton, the greater the masses of interacting
objects, the

a) greater the force of gravity, by the product of the massesF_{g}= G M m / d^{2}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

32. 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 thesquareof the distanceF_{g}= G M m / d^{2}

33. If the mass of Earth somehow increased with no change in radius,
your weight would

a) increaseF_{g}= G M m / d^{2}b) decrease

c) stay the same

34. If the radius of Earth somehow decreased with no change in mass,
your weight would

a) increaseF_{g}= G M m / d^{2}b) decrease

c) stay the same

35. 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 valueF_{g}= G M m / d^{2}c) increase to nine times its original value

d) increase to three times its original value

36. 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 surfaceF_{g}= G M m / d^{2}

d, the distance from thecenterof Earth to the Space Shuttle, is not very different from the radius of Earth.c) about one-tenth its weight at Earth's surface

d) about one-one hundredth its weight at Earth's surface

37. 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 NF_{g}= G M m / d^{2}

On the tower, d, the distance from the center of Earth to the top of the tower is 2R_{e}, twice the radius of Earth.c) 200 N

d) 800 N

38. 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 weightF_{g}= G M m / d^{2}

d is the distance from thecenterof Earth to the apples.d) twice the weight

39. 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.This was one of the homework problems.d) you are 100 times more weightless there.

40. 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

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

a)~~cylinder~~(that should have been "hoop"

b) sphereThe sphere has more mass nearer to its axis of rotation so its "rotational mass" is smaller and, therefore, it is easier to rotate.c) neither; they both reach the bottom at the same time

42. 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

43. When a twirling ice skater **extends** her arms
**out**ward, her rotational speed

a) increases

b) decreases

c) remains the same (ie,it is conserved).

44. A 3.0-kg cart, initially moving to the **right** at
v_{1i} = 2.0 m/s, collides with a 1.0-kg cart, initially at
**rest** (v_{2i} = 0). The collision is totally
**elastic**. After the collision, the carts have final velocities
of

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

45. A 1-kg rock is suspended from the tip of a meter stick at the 0 cm mark so that the meter stick balances like a see-saw when the fulcrum is at the 25-cm mark. From this information, what is the mass of the meter stick?

a) 0.25 kg

b) 0.50 kg

c) 1.00 kg.

d) 2.00 kg

46. 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 curveThis is known as the centripetal force.c) zero because the car is not accelerating.

d) directed outward, away from the center of the curve

47. 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.

48. 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 thanAnincreasein distance means adecreasein force.b) the same as

c) more than

if you were not wearing seat belts.

49. 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.

50. A diver does a double saumersalt and then extends his body so
that his rotation nearly stops before going into the water. This is
an example of conservation of

a) momentum.

b) kinetic energy.

c) potential energy.

d) angular momentum.