Suppose that a rock is swinging in a circle when some string is let out so that the length doubled as the same speed is maintained.The force now exerted on the string is
A)the same as before.
B)doubled.
C)half as great.
D)four times as great.

Question

Quizplus · Accepted Answer

The force exerted on the string is directly proportional to the tension in the string, which is given by T=mv²/r, where m is the mass of the rock, v is its velocity, and r is the radius of the circle. When the string is let out so that the length doubles, the radius of the circle also doubles, and therefore, the tension in the string is reduced by a factor of two. Thus, the force exerted on the string is also reduced by a factor of two, and the correct choice is (C).

Suppose That a Rock Is Swinging in a Circle When