Download Gravitational Force, Torque and Simple Machines Multiple Choice

Gravitational Force, Torque and Simple Machines
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. Calculate the mechanical advantage of a wrench that allows you to move a bolt 0.01 m by moving
the handle 0.50 m.
a. 0.05
b. 0.50
____
c. 5.0
d. 50
2. A ramp is a ____________ that decreases the force required to move an object while increasing the
distance the object travels.
a. machine
b. force
____
3. What is the mechanical advantage of a ramp 2.0 m long and 0.50 m tall?
a. 1.0
b. 2.5
____
c. load
d. newton
c. 4.0
d. None of the above
4. A pulley with a mechanical advantage of 5.00 is used to lift a bucket weighing 285 N. How much
force must be used to lift the bucket?
a. 57.0 N
b. 285 N
____
c. 280 N
d. 1,425 N
5. Lifting a car using a car jack is easier because it requires
a. less force.
b. less work.
c. less time.
d. None of the above
____
6. Tides are caused by
a. differences in the gravitational force of the sun at different points on Earth.
b. differences in the gravitational force of the moon at different points on Earth.
c. differences in Earth’s gravitational field strength at different points on Earth’s surface.
d. fluctuations in the gravitational attraction between Earth and the moon.
____
7. Why does an astronaut weigh less on the moon than on Earth?
a. The astronaut has less mass on the moon.
b. The astronaut is farther from Earth’s center when he or she is on the moon.
c. The gravitational field strength is less on the moon’s surface than on Earth’s surface.
d. The astronaut is continually in free fall because the moon orbits Earth.
____
8. An object’s tendency to resist acceleration is measured by the object’s
a. gravitational mass.
c. gravitational field strength.
b. inertial mass.
d. weight.
____
9. The degree to which an object attracts other objects is measured by the object’s
a. gravitational mass.
c. gravitational field strength.
b. inertial mass.
d. weight.
____ 10. Which of the following confirms that gravitational mass and inertial mass are equivalent?
a. Free-fall acceleration is the same throughout the universe.
b. Free-fall acceleration is the same at all points where the gravitational field strength is the
same.
c. Newton’s second law is valid throughout the universe.
d. An object’s weight can change with location, but the object’s mass remains constant.
____ 11. In this text, which of the following symbols represents gravitational field strength?
a. F
c. g
b. G
d. F
____ 12. In this text, which of the following symbols represents the constant of universal gravitation?
a. F
c. g
b. G
d. F
____ 13. Which of the following equations expresses Newton’s law of universal gravitation?
a.
c.
b.
d.
____ 14. When calculating the gravitational force between two extended bodies, you should measure the distance
a. from the closest points on each body.
b. from the most distant points on each body.
c. from the center of each body.
d. from the center of one body to the closest point on the other body.
____ 15. The gravitational force between two masses is 36 N. What is the gravitational force if the distance between
them is tripled? (G = 6.673  10 Nm /kg )
a. 4.0 N
c. 18 N
b. 9.0 N
d. 27 N
____ 16. Two small masses that are 10.0 cm apart attract each other with a force of 10.0 N. When they are 5.0 cm
apart, these masses will attract each other with what force?
(G = 6.673  10 Nm /kg )
a. 5.0 N
c. 20.0 N
b. 2.5 N
d. 40.0 N
____ 17. Which of the following quantities measures the ability of a force to rotate or accelerate an object around an
axis?
a. axis of rotation
c. tangential force
b. lever arm
d. torque
____ 18. Where should a force be applied on a lever arm to produce the most torque?
a. closest to the axis of rotation
b. farthest from the axis of rotation
c. in the middle of the lever arm
d. It doesn’t matter where the force is applied.
____ 19. If you want to open a swinging door with the least amount of force, where should you push on the door?
a. close to the hinges
c. as far from the hinges as possible
b. in the middle
d. It does not matter where you push.
____ 20. If you cannot exert enough force to loosen a bolt with a wrench, which of the following should you do?
a. Use a wrench with a longer handle.
b. Tie a rope to the end of the wrench and pull on the rope.
c. Use a wrench with a shorter handle.
d. You should exert a force on the wrench closer to the bolt.
____ 21. Suppose a doorknob is placed at the center of a door. Compared with a door whose knob is located at the
edge, what amount of force must be applied to this door to produce the torque exerted on the other door?
a. one-half as much
c. one-fourth as much
b. two times as much
d. four times as much
____ 22. A heavy bank-vault door is opened by the application of a force of 3.0  10 N directed perpendicular to the
plane of the door at a distance of 0.80 m from the hinges. What is the torque?
a. 120 Nm
c. 300 Nm
b. 240 Nm
d. 360 Nm
____ 23. If the torque required to loosen a nut on a wheel has a magnitude of 40.0 Nm and the force exerted by a
mechanic is 133 N, how far from the nut must the mechanic apply the force?
a. 1.20 m
c. 30.1 cm
b. 15.0 cm
d. 60.2 cm
____ 24. What kind of simple machine are you using if you pry a nail from a board with the back of a hammer?
a. a wedge
c. a lever
b. a pulley
d. a screw
____ 25. A girl pushes a box that has a mass of 450 N up an incline. If the girl exerts a force of 150 N along the incline,
what is the mechanical advantage of the incline?
a. 0.33
c. 300
b. 3.0
d. 33%
____ 26. Which of the following is not a valid equation for mechanical advantage?
a.
c.
b.
d.
____ 27. An iron bar is used to lift a slab of cement. The force applied to lift the slab is 4.0  10 N. If the slab weighs
6400 N, what is the mechanical advantage of the bar?
a. 1.6
c. 6000
b. 16
d. 6.3%
____ 28. What is the efficiency of a machine that requires 1.00  10 J of input energy to do 35 J of work?
a. 2.9%
c. 35%
b. 29%
d. 65%
____ 29. A box weighing 210 N is pushed up an inclined plane that is 2.0 m long. A force of 140 N is required. If the
box is lifted 1.0 m, what is the efficiency of the inclined plane?
a. 33%
c. 67%
b. 50%
d. 75%
____ 30. What quantity measures the output force of a machine relative to the input force?
a. torque
c. mechanical advantage
b. leverage
d. efficiency
____ 31. What quantity measures the work done by a machine relative to the work done on a machine?
a. torque
c. mechanical advantage
b. leverage
d. efficiency
Problem
32. A lever with an output distance of 0.6 m has a mechanical advantage of 8. What is the length of the input
distance?
33. A ramp with a mechanical advantage of 5 is used to move a crate that weighs 210 N. What force is needed to
push the crate up the ramp?
34. A 69.8 kg student sits at a desk 1.75 m away from a 78.9 kg student. What is the magnitude of the
gravitational force between the two students? (G = 6.673  10 Nm /kg )
35. Two trucks with equal mass are attracted to each other with a gravitational force of 5.3  10 N. The trucks
are separated by a distance of 2.6 m. What is the mass of either of the trucks? (G = 6.673  10 Nm /kg )
36. A bucket filled with water has a mass of 33 kg and is attached to a rope wound around a cylinder with a radius
of 0.043 m at the top of a well. What torque does the weight of the water and bucket produce on the cylinder?
(g = 9.81 m/s )
37. To warm up before a game, a baseball pitcher tosses a 0.146 kg ball by rotating his forearm, which is 0.33 m
in length, to accelerate the ball. The ball starts at rest and is thrown at a speed of 18 m/s in 0.47 s. While the
ball is in the pitcher’s hand, what torque is applied to the ball to produce the final tangential speed?
38. A child with a weight of 2.56  10 N sits on a seesaw 0.41 m from the axis of rotation. How far from the axis
of rotation on the other side should a child with a weight of 5.16  10 N sit so the seesaw will remain
balanced?
39. A 4.2 m board with a mass of 19 kg is pivoted at its center of gravity. A helium balloon attached 0.24 m from
the left end of the board produces an upward force of 7.1 N. A 3.5 kg book is placed 0.74 m from the left end
of the board, and another book of 1.7 kg is placed 0.77 m from the right end of the board. Find the torque on
the board and the direction of rotation.
40. A boy can raise a rock that weighs 95 N by using a lever and applying a force of 17 N. What is the
mechanical advantage of the lever?
41. A force of 1050 N is needed to move a crate weighing 3050 N up a ramp that is 3.89 m long. If the elevated
end of the ramp is 0.770 m high, what is the efficiency of the ramp?
42. What is the efficiency of a machine that requires 156 J of input energy to do 91.9 J of work?
43. How much energy would be required to do 971 J of work with a machine that was 25% efficient?
PROBLEM
32. ANS:
4.8 m
PTS: 1
33. ANS:
42 N
PTS: 1
34. ANS:
Given
Solution
PTS: 1
35. ANS:
7.3  10 kg
Given
Solution
DIF: IIIA
OBJ: 7-2.2
PTS: 1
36. ANS:
14 Nm
DIF: IIIC
OBJ: 7-2.2
DIF: IIIA
OBJ: 7-4.2
DIF: IIIB
OBJ: 7-4.2
Given
Solution
PTS: 1
37. ANS:
1.8 Nm
Given
Solution
PTS: 1
38. ANS:
0.20 m
Given
Solution
PTS: 1
DIF: IIIB
39. ANS:
13 Nm counterclockwise
Given
Solution
OBJ: 7-4.2
PTS: 1
40. ANS:
5.6
DIF: IIIC
OBJ: 7-4.2
DIF: IIIA
OBJ: 7-4.4
DIF: IIIB
OBJ: 7-4.4
Given
Solution
PTS: 1
41. ANS:
57.5%
Given
Solution
PTS: 1
42. ANS:
58.9%
Given
Solution
PTS: 1
43. ANS:
DIF: IIIA
OBJ: 7-4.4
DIF: IIIB
OBJ: 7-4.4
Given
Solution
PTS: 1