Question
A string 0.5 m long is used to whirl a 1 kg stone in a vertical circle at a uniform velocity of 5 m s-1. What is the tension in the string when the stone is at the top of the circle?
9.8 N
30.4 N
40.2 N
59.8 N
Solution
C.
40.2 N
The centripetal force needed to keep the stone moving at 5 m s-1 is
Fc =
=
Fc = 50 N
The weight of the stone is
W = m g
= ( 1 kg ) ( 9.8 m s-2 )
W = 98 N
At the top of the circle
T = Fc 98 N
T = 40.2 N
