Excursions in Physics
PHY
3050C
Second Hour Exam
October 12, 1999
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.
For every question, also consider the following as a possible
answer:
e) none of the above
Possibly useful information:
v =x /
t
a =v /
t
v = vi + a t
x = xi + vi t + (1/2) a t2
v = r
F = m a
F12 = &endash; F21
w = mg
g = 9.8 m/s210 m/s2
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.The tightrope walker has some momentum.b) a truck speeding along a highway.
p = m vThis speeding truck has more mass and greater velocity
than the tightrope walker of option a).
c) a Mack truck sitting in the parking lot.
With no velocity, the Mack truck has no momentum.d) the Science building on campus.
With no velocity, the building has no momentum.
2. A moving object on which no forces are acting will continue to move with constant
a) accelerationb) impulse
c) momentum
Constant velocity means constant momentum.d) all of these
3. Conservation of momentum is directly related to
a) Newton's First Law of Motionb) Newton's Second Law of Motion
c) Newton's Third Law of Motion
d) International shortages of momentum
4. 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 of the rifle is smaller than that of the bullet.
c) mass of the rifle is much larger than the mass of the bullet.
d) momentum of the rifle is larger than that of the bullet.
5. 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) speedb) acceleration
c) momentum
d) all of the above
6. A 5 kg ball has a momentum of 30 kg m/s. What is the ball's speed?
a) 3 m/sb) 6 m/s
p = m v30 kg m/s = (5 kg) ( v )
30 kg m/s = (5 kg) ( 6 m/s )
v = 6 m/s
c) 15 m/s
d) 150 m/s
7. If two objects collide and do not stick together, their total momentum after the collision is
a) less thanb) 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 thanb) 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.
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, vb) kinetic energy, KE
c) angular velocity, w
d) work, W
11. Work involves
a) mass multiplied by accelerationb) 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.
Work = force x distanceWork = force x distance
Increasing the distance by two also increased the work by the same factor of two.
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.
Work = force x distanceWork = force x distance
Increasing the force by two also increased the work by the same factor of two.
d) four times as much work.
14. Exert 4 N for a distance of 3 m in 2 s and you deliver a power of
a) 2.0 Wb) 4.0 W
c) 6.0 W
P = W/tP = [ ( 4 N ) ( 3 m ) ] / [ 2 s ]
P = 12 N m / 2 s
P = 12 J / 2 s
P = 6 W
d) 8.0 W
15. Exert 2,000 J of work in 50 s and your power output is
a) 5 Wb) 10 W
c) 20 W
d) 40 W
P = W / tP = 2,000 J / 50 s
P = 40 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 energyb) the same amount of energy
c) twice as much energy
PE = m g hPE = m g h
Increasing h by a factor of 2 also increases PE by a factor of 2.
d) four times as much energy
17. An object that has kinetic energy must be
a) elevatedb) falling
c) moving
KE = ( 1/2 ) m v2d) at rest
18. An object that has potential energy may have this energy because of its
a) speedb) acceleration
c) momentum
d) position
19. When a car is braked to a stop, its kinetic energy is transformed to
a) energy of motionb) 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) PE = m g h
21. For which position above does the ball on the end of the string have the greatest kinetic energy?
d) Etotal = PE + KE = constantPE = min at position DThat means
KE = max at position D
22. A 10 kg sack is lifted 2 meters in the same time as a 5 kg sack is lifted 4 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 muchb) the same
P = W / tW1 = m g h 1 = (10 kg) ( 10 m/s2) ( 2 m) = 200 J
W2 = m g h 2 = ( 5 kg) ( 10 m/s2) ( 4 m) = 200 J
W1 = W2 and t1 = 22
Therefore,
P1 = P2
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 Jb) 75 J
c) 150 J
PE = m g hPE = ( 3 kg ) ( 10 m/s2 ) ( 5 m )
PE = 150 J
d) 300 J
24. A 5 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 mb) 1 m
PE = m g h50 J = ( 5 kg ) ( 10 m/s2 ) ( h )
50 J = ( 5 kg ) ( 10 m/s2 ) ( 1 m )
h = 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 energyb) 3 times the kinetic energy
c) 9 times the kinetic energy
KE = ( 1/2 ) m v2KE1 = ( 1/2 ) m v12
KE2 = ( 1/2 ) m ( 3 v1 )2
KE2 = 9 ( 1/2 ) m v12
KE2 = 9 KE1
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 mb) 90 m
c) 120 m
d) 180 m
KE = ( 1/2 ) m v2Increasing the speed from 40 km/hr to 120 km/hr
is an increase in speed by a factor of three.
That means an increase in the KE by a factor of NINE.
Work = change in KE
This means the work done in bringing the car to a stop increases by a factor of NINE.
Work = force x distance
If the work increases by a factor of nine, the distance must also increase by a factor of nine.
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 energyb) 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
It can have potential energy while it is at rest.c) mass
It always has mass.d) all of the above
29. If an object has kinetic energy, then it also must have
a) momentumb) velocity
c) speed
d) all of the above
30. According to Kepler's laws, the paths of planets about the Sun are
a) straight linesb) parabolas
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 m1 m2 / r2b) 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 distanceb) 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 m1 m2 / r2
33. If the mass of Earth somehow decreased with no change in radius, your weight would
a) increaseb) decrease
F = G m1 m2 / r2c) stay the same
34. If the radius of Earth somehow decreased with no change in mass, your weight would
a) increaseF = G m1 m2 / r2b) 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 valueb) decrease to one-third its original value
F = G m1 m2 / r2Changing m1 to one-third its original value will change F to one-third its value.
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) zerob) equal to the weight of the Space Shuttle at Earth's surface
In a low-Earth orbit, the value for r in Newton's Law of Gravity,F = G m1 m2 / r2 , is not much different than r 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
37. A woman who normally weighs 500 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) zerob) 125 N
At a distance of TWO Earth radii, her weight is one-fourth what it is at a distance of ONE Earth radius.c) 250 N
d) 500 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 weightb) one-half the weight
c) the same weight
The distance r in F = G m1 m2 / r2 is measured from the CENTER of Earth and that is nearly the same for all these 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.
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 axisb) 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 or ring or hoopb) sphere
For the same mass and radius, the sphere has a smaller "rotational mass" (or moment of inertia), so 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) twob) four
c) eight
d) sixteen
43. When a twirling ice skater extends her arms outward, her rotational speed
a) increasesb) decreases
Extending her arms INCREASES her rotational mass.Angular momentum = (rotational mass) x (rotational speed)
Angular momentum = constant
(rotational mass) x (rotational speed) = (rotational mass) x (rotational speed)
c) remains the same (ie, it is conserved).
44. To turn a stubborn screw, it is best to use a screwdriver that has a handle that is
a) long and thinb) thick or wide
c) yellow
d) slippery
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 kgb) 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 net force has a special name, 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 thanb) 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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