b.
How much work is done by the cord in one revolution? Explain how you arrived at your answer.
c.
The speed of the ball is determined to be 3.7 m/s. Assuming that the cord is horizontal as it swings,
calculate the expected tension in the cord.
d.
The actual tension in the cord as measured by the spring scale is 5.8 N. What is the percent difference
between this measured value of the tension and the value calculated in part c?
e.
The students find that, despite their best efforts, they cannot swing the ball so that the cord remains exactly
horizontal.
i. On the picture of the ball below, draw vectors to represent the forces acting on the ball and identify the
force that each vector represents.
AP FR QUIZ #21 CENTRIPITAL MOTION
1975B1. A 2-kilogram block is released from rest at the top of a curved incline in the shape of a quarter of a
circle of radius R. The block then slides onto a horizontal plane where it finally comes to rest 8 meters from the
beginning of the plane. The curved incline is frictionless, but there is an 8-newton force of friction on the block
while it slides horizontally. Assume g = 10 meters per second2.
a. Determine the magnitude of the acceleration of the block while it slides along the horizontal plane.
a)
Fnet = ma
– fk = ma
–8=2a
a = – 4 m/s2
b.
What time elapses while the block is sliding horizontally?
(b) vf2 = vi2 + 2ad (0)2 = vi2 + 2(
vf = vi+ at
c.
– 4)(8)
vi = 8 m/s
t = 2 sec
Calculate the radius of the incline in meters. (radius is the height.)
Utop = Kbot
mgh = ½ mv2
(10)(h) = ½ (8)2 h= R = 3.2 m
1997B2. To study circular motion, two students use the hand-held device shown above, which consists of a rod
on which a spring scale is attached. A polished glass tube attached at the top serves as a guide for a light cord
attached the spring scale. A ball of mass 0.200 kg is attached to the
other end of the cord. One student swings the teal around at constant
speed in a horizontal circle with a radius of 0.500 m. Assume friction
and air resistance al negligible.
a. Explain how the students, by using a timer and the information
given above, can determine the speed of the ball as it is revolving.
ii. Explain why it is not possible for the ball to swing so that the cord remains exactly horizontal.
If the roadway is properly banked, the box will still remain in place on the truck for the same speed v even when the truck bed is
frictionless.
c.
On the diagram below indicate and clearly label the two forces acting on the box under these conditions
d.
Which, if either, of the two forces acting on the box is greater in magnitude?
iii. Calculate the angle that the cord makes with the horizontal.
1977 B2. A box of mass M, held in place by friction, rides on the flatbed of a truck which is traveling with
constant speed v. The truck is on an unbanked circular roadway having radius of curvature R.
a. On the diagram provided above, indicate and clearly label all the force vectors acting on the box.
b.
Find what condition must be satisfied by the coefficient of static friction  between the box and the truck bed. Express your
answer in terms of v, R, and g.