Name __________________________________________
AP Physics Summer Work
Rotational Mechanics – Torque
(1)
For Questions 1 – 5, A = True & B = False
The distance between a turning axis and the point of contact of a perpendicular
force is called the fulcrum.
1) ______
(2)
Torque is the product of a force exerted on an object times the lever arm.
2) ______
(3)
In order for a seesaw to be in rotational equilibrium, the sum of the torques acting
on it need not be balanced if one person sits closer to the fulcrum than the other person.
3) ______
(4)
Torque is defined as tangential force times mass.
4) ______
(5)
Suppose you try loosening a nut with a wrench, and the nut doesn't give at all. You increase 5) ______
your chance of success if you exert a larger force.
(6)
A heavy boy and a light girl are balanced on a mass-less seesaw. If they both move
forward so that they are one-half their original distance from the pivot point, what will
happen to the seesaw?
A) The side the girl is sitting on will tilt downward.
B) The side the boy is sitting on will tilt downward.
C) The seesaw will start rotating counter-clockwise.
D) Nothing, the seesaw will still be balanced.
6) ______
(7)
A vault is opened by applying a force of 300 N perpendicular to the plane of the door,
0.8 m from the hinges. Find the torque due this force about an axis through the hinges.
A) 120 N-m
B) 240 N-m
C) 300 N-m
D) 360 N-m
7) ______
(8)
A meter stick is supported by a knife edge at the 0.5 m mark. Ryan hangs masses of
0.40 kg and 0.60 kg from the 0.2 m and 0.8 m marks, respectively. Where should Ryan
hang a third mass of 0.30 kg to keep the stick balanced (rotational equilibrium)?
A) 0.15 m
B) 0.20 m
C) 0.25 m
D) 0.30 m
8) ______
(9)
Two equal forces are applied to a door. The first force is applied at the midpoint of the
door; the second force is applied at the doorknob. Both forces are applied perpendicular
to the door. Which force exerts the greater torque?
A) both exert equal non-zero torques
B) the first at the midpoint
C) the second at the doorknob
D) both exert zero torques
9) ______
Page 2
(10)
The bolts on a car wheel require tightening to a torque of 90 Nm. If a 0.3-m long wrench
is used, what is the magnitude of the force required when the force is perpendicular to the
wrench?
A) 150 N
B) 30 N
C) 300 N
D) 15 N
10) ______
(11)
A 60-kg boy sits on a seesaw 1.0 m from the fulcrum. What distance from the fulcrum
should a 30-kg girl should sit in order to balance the seesaw?
A) 1.3 m
B) 2.0 m
C) 2.5 m
D) 3.0 m
11) ______
(12)
Mary pushes a metal pipe 1.5 m out past the edge of a building so that it is just perfectly
12) ______
balanced from tipping over while a basket weighing 100 N hangs on the end. If the uniform
pipe weighs 200 Newtons how far away from the edge is the center of gravity of the pipe located?
A) 0.50 m
B) 0.75 m
C) 1.25 m
D) 1.50 m
(13)
A bucket filled with water has a mass of 23 kg and is attached to a rope that is wound
around a cylinder with a diameter of 0.10 meters at the top of the well. What torque does
the weight of the water and bucket produce on the cylinder? (g = 9.8 m/s2)
A) 34 N – m
B) 23 N – m
C) 17 N – m
D) 11 N – m
13) ______
Page 3
(14)
Jack and Jill are sitting on opposite sides of a seesaw; each 2 meters from the fulcrum. If
Jack has a mass of 60 kg and Jill has a mass of 50 kg how far can Mighty Mutt (mass =
25 kg) sit from Jill so that all are in rotational equilibrium?
A) 0.8 m
B) 1.0 m
C) 1.2 m
D) 1.6 m
14) ______
(15)
If a clockwise force is applied a perpendicular distance from a pivot point in the plane of
this paper, what is the direction of the resultant torque vector?
A) clockwise
B) toward the top of this paper
C) perpendicular and into the paper
D) perpendicular and out of the paper
15) ______
(16)
A uniform board that weighs 500 N is supported by two bricks. Two bricks, one at each
16) ______
end of the board, support the board. If the board is 3 meters long and a sack of sand weighing
400 Newtons is located 0.5 meters from the middle of the board, how much weight does each
brick support?
A) 900 N and 517 N
B) 383 N and 517 N
C) 383 N and 450 N
D) 1550 N and 900 N
(17)
Morgan and Abby have a uniform pole that is 2 meters long and weighs 50 Newtons. The
girls are to carry a 100 Newton backpack hanging from the pole from one class to another.
While Morgan isn’t looking Abby shifts the backpack so that the backpack is only 75 cm
(0.75 m) from Morgan. If the ends of the pole are supported by the girls how much weight
does Morgan carry?
A) 87.5 N
B) 62.5 N
C) 150 N
D) 75.0 N
17) ______
Page 4
(18)
A utility pole that lies on the ground weighs 4000 Newtons is non-uniform and 10 m long. 18) ______
If the center of mass for the pole is 2 meters from the heavier end and Carl wants to pick up
the lighter end of the pole, what is the minimum force he will have to use?
A) 4000 N
B) 100 N
C) 500 N
D) 800 N
(19)
When Kin opens a door for his mother he pulls the door handle with a force of 20 Newtons. 19) ______
If his arms make a 30 angle with the door and the door handle is 0.9 meters from the door
hinges, how much torque does Kin exert on the door?
A) 9 N – m
B) 45 N – m
C) 4.5 N – m
D) 16 N – m
(20)
A pulley with a diameter of 20 centimeters has a 500 gram mass tied to a string that passes
over the pulley and is just hanging. What torque is the mass exerting on the pulley?
A) 9.8 N – m
B) 0.98 N – m
C) 490 N – m
D) 0.49 N – m
20) ______