2008 Dept. Natural Resources: General Physics test 03 (2008/12/29) Name:__________ ID:__________
Multiple Choice Identify the choice that best completes the statement or answers the question.
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1. The diagrams below show forces applied to a wheel that weighs 20 N. The symbol W stands for the weight. In
which diagram(s) is the wheel in equilibrium?
A) A
B) B
C) C
D) D
E) A and C
2. Sebastian has drawn a free-body diagram for a ladder of mass m leaning against a frictionless wall. His diagram is
shown below.
A)
is in the wrong direction.
B)
C)
D)
should be directed upwards, not down.
should be perpendicular to the wall, not parallel to it.
should be down into the floor for
to have the given direction.
E)
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is correct, but there should also be a force perpendicular to the wall.
3. Consider standing next to a house where the lawn slopes down from left to right.
You need to climb up a ladder to paint this side of the house, but only the left side of the ladder is touching the
ground. You should:
A) proceed since the ladder is in equilibrium.
B) dig a hole for the left side until both legs are supported.
C) insure that the left leg is free to move before climbing the ladder.
D) place wood blocks under the right side until both legs are supported.
E) tie a rope to the top of the ladder to maintain a constant tension to
the right and a uniform clockwise torque upon the ladder.
4. A small branch is wedged under a rock and rests on a smaller object. The smaller object is 2.0 m from the large
rock and the branch is 10.0 m long. If the mass of the branch is 20.0 kg, what force must be exerted on the smaller
rock?
B) 490 N
C) 50 N
D) 200 N
A) 49 N
5. An irregularly shaped object 10 m long is placed with each end on a scale. If the scale on the right reads 74 N and
the scale on the left reads 93 N. how far from the left is the center of gravity.
A) 8.0 m
B) 5.6 m
C) 13 m
D) 4.4 m
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6. A 200-kg nonuniform beam, 6.0 m long, is loosely pinned at the pivot at P. A
600-kg block is suspended from the end of the boom at A. The boom forms a
30° angle with the horizontal, and is supported by a cable, 4.0 m long, between
points D and B. Point B is 4.0 m from P, and point D is 4.0 m above P. The
center of mass of the boom is at point C, which is 2.0 m from P.
In the figure, the tension in the cable is closest to:
A) 9000 N B) 9800 N C) 7800 N D) 8800 N E) 8300 N
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7. A uniform 200-kg beam, 6 m long, is freely pivoted at P. The beam is supported in a
horizontal position by a light strut, 5 m long, which is freely pivoted at Q and is
loosely pinned to the beam at R. A load of mass is suspended from the end of the
beam at S. A maximum compression of 22,000 N in the strut is permitted, due to
safety. In the figure, under maximum load the y-component of the force exerted on
the beam by the pivot at P is closest to:
A) 5620 N B) 8800 N C) 7820 N D) 10,020 N E) zero
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8. A metal crowbar is 2.00 m long and has a mass of 5.00 kg. Its center of mass is located 0.60 m from the "bottom"
end. The bar is pivoted over a pipe 0.10 m from the tip, with the tip pushing up on a rock. A person pushes down
on the other end of the bar with a force of 100 N. The bar is horizontal. The rock was not moved. To have a better
chance to move the rock, the person could:
A) apply more force.
B) move the pipe so it is closer to the rock.
C) move the pipe so that it is further from the rock.
D) both a and b.
E) both a and c.
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9. A 20-kg uniform door has a width of 1.2 m and a height of 2.5 m. The door is mounted on a post by a pair of
hinges, marked 1 and 2, at the top and bottom of the door. An external force of 60 N, at an angle of 30° above the
horizontal, is applied to the doorknob, as shown. The doorknob is 1.0 m above the bottom of the door.
In the figure, the sum of the y-components of the forces, exerted on the door by hinges 1 and 2, is closest to:
A) 165 N
B) 195 N
C) 145 N
D) 250 N
E) 225 N
____ 10. In the figure, the Achilles tendon exerts a force F = 720 N. What is the torque it exerts
about the ankle joint?
A) 21.2 N · m B) 16.2 N · m C) 36.0 N · m D) 25.9 N · m E) 12.2 N · m
____ 11. Suppose that a heavy person and a light person are balanced on a teeter-totter made of a
plank of wood. Each person now moves in toward the fulcrum a distance of 25 cms.
What effect will this have on the balance of the teeter-totter?
A)
B)
C)
D)
The heavy person's end will go down.
The teeter-totter will remain in balance.
The light person's end will go down.
One cannot tell whether either end will rise or fall without knowing the relative mass of
the plank.
E) Only if the plank has significant mass will the light person's end go down.
____ 12. A body is in equilibrium when
A) the sum of the forces is zero.
B) angular momentum is zero.
C) the sum of the torques is zero.
D) the sum of the torques is zero and the sum of the forces is zero.
E) the sum of the torques is zero and angular momentum is zero.
____ 13. A ladder of mass m leans against a frictionless wall that exerts a normal force P on the ladder. The coefficient of
static friction between the ground and the ladder is  s . The magnitude of the normal force the ladder exerts on
the ground is
A)  s mg .
B) mg .
C) P.
D)  s P .
E)  s mg  P .
b
g
____ 14. John is carrying a shovelful of snow. The center of mass of the 3.00 kg of snow he is holding is 15.0 cm from the
end of the shovel. He is pushing down on the opposite end of the shovel with one hand and holding it up 30.0 cm
from that end with his other hand. Ignore the mass of the shovel. Sarah says that his hand pushing down on the
shovel must be exerting a greater force than the hand pushing up. James says it is just the reverse. Which one, if
either, is correct?
A) Sarah, because the hand pushing down must exert a greater force to match the torque
exerted by the snow.
B) James, because, depending on the location of the axis of rotation, the hand pushing down
can counteract the torque exerted by the snow.
C) James, because the hand pushing up must exert a force that equals the sum of the force of
the hand pushing down and the weight of the snow.
D) James, because both (b) and (c) above are correct.
E) Neither, because the hands exert forces of equal magnitudes.
____ 15. A system consisting of a basketball at rest on the floor at center court is:
A) in stable equilibrium.
C) in unstable equilibrium. E) not in equilibrium.
B) in neutral equilibrium.
D) in equilibrium with net force equal to 0, but with a non-zero net torque.