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Physics 512
Name ________________________
Circles & Torque
vc = 2πr
T
ac= v2/r
Fc= mac
t= F*L
1) In order to go in a circle, a _______________________ must act which is directed
towards __________________________. The velocity of an object traveling in a circle is
always directed _____________________ to the circle.
2) How can we say that an object moves at a constant speed around a circle even though
we also say it is accelerating?
_______________________________________________________________________
_______________________________________________________________________
3) The diagram below shows an overhead view of a child swinging a toy plane in a circle
above her head by a rope at a constant speed in a counterclockwise direction. The picture
shows the toy plane (represented by a grey blob) at two different locations A and B.
N
B
W
E
A
S
a) At position A, what is the direction of the velocity? _______; the acceleration? ______
b) At position B, what is the direction of the velocity? _______; the net force? ________
c) If the rope were cut when the plane were at point A, describe the motion that results.
________________________________________________________________________
d) In this situation, what force acts as the centripetal force? ______________________
3) When you are rounding a corner in a car, it feels like you are being pushed outwards.
Some people call it the ‘centrifugal force.’ Some people would also be wrong. What
causes this feeling?
________________________________________________________________________
________________________________________________________________________
Questions 16-19 refer to an object that is being twirled in a clockwise circle at he end of a
string as shown in the diagram.
4. ______ At the moment shown in the diagram,
the object’s velocity is towards point
A B C D
5. ______ At the moment shown in the diagram,
the force acting on the object is towards
A B C D
6.______ If the string breaks at this moment, the object would travel towards point
A B C D
7. ______ If the speed of the object was increased, the period of rotation would
a) increase b) decrease c) remain the same
8. If all the forces acting on the wrench are the same size, which will be the one that will
most easily turn the bolt? Why?
________________________________________________________________________
________________________________________________________________________
F4
F1
F2
F3
9) A 5 kg bucket is attached to a string a whirled in a perfectly horizontal circle above a
person’s head. The length of the string is 2 meters. The speed of the bucket is a constant 4
m/s.
a) What is the period of the bucket’s motion?
b) What is the centripetal acceleration of the bucket?
c) What is the tension in the string?
d) How many revolutions does the bucket make in one minute?
e) What is the angle between the directions of the velocity and acceleration at any
moment for the bucket?
10. Henry and Jane want to play on the seesaw. Henry has a mass of 50 kg and Jane has
a mass of 40 kg. The pivot point of the seesaw is at the center as shown. If Henry sits on
the right side 3 meters from the pivot point, where should Jane sit to balance the seesaw?
Solve the problem and indicate on the diagram.
11 . A mobile is hanging as shown. If the system is in rotational equilibrium, what must
be the mass of the box on the right?
30 cm
20 kg
50 cm