3050Ex2F00

Eastern Illinois University
Doug Davis
DDavis@eiu.edu
217.581.6346

PHY 3050C
Excursions in Physics
“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 v

c) a Mack truck sitting in the parking lot. While the mass is large, the velocity is zero.
d) the Science building on campus.While the mass is even larger, the velocity is still zero.

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

a) acceleration
b) impulse
c) momentum
F = m a
F = 0 means a = 0

a = 0 means v = const

v = const means p = m v = constant

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
We used F₁₂ = - F₂₁ 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/s
P = m v
30 kg m/s = (5 kg) (6 m/s)

v = 6 m/s

c) 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 (ie, they stick together). What is their commong final velocity?

a) 0.33 m/s.
Initially, before the collision,
P_Tot,i = m₁ v_1i + m₂ 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, after the collision,

P_Tot,f = ( 3 kg ) ( v_f )

Conservation of momentum tells us these two valus of the total momentum are the same,

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/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 commong final velocity?

a) - 0.33 m/s (ie, to the left).
Initially, before the collision,
P_Tot,i = m₁ v_1i + m₂ 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, after the collision,

P_Tot,f = ( 3 kg ) ( v_f )

Conservation of momentum tells us these two valus of the total momentum are the same,

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/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
Momentum is always conserved!

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
Momentum is always conserved!

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, KE
Boing!

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 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 W
P = 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 W
P = 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 energy
PE_grav = m g h

d) four times as much energy

17. An object that has kinetic energy must be

a) elevated
b) falling
c) moving
KE = ¹/₂ m v²

d) at rest

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

a) speed
b) acceleration
c) momentum
d) position
PE_grav = m g h is an example

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 A
PE_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 D
PE_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 m
Traveling 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) momentum
p = m v

b) 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 with projectile 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 masses
F_g = G M m / d²

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 the square of the distance
F_g = G M m / d²

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

a) increase
F_g = G M m / d²

b) decrease
c) stay the same

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

a) increase
F_g = G M m / d²

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 value
F_g = G M m / d²

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 surface
F_g = G M m / d²
d, the distance from the center of 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 N
F_g = G M m / d²
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 weight
F_g = G M m / d²
d is the distance from the center of 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) sphere
The 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 outward, 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 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

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 than
An increase in distance means a decrease in 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.

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