A girl whirls a ball on the end of a string above her head. Assume the motion of

Question

A girl whirls a ball on the end of a string above her head. Assume the motion of her hand to keep the ball in motion is negligible. For the ball to remain in a circular path while it rotates with a constant speed, which of the following is true?

  (     ) In addition to the centripetal force shown in the figure, there must also be a centrifugal force that pulls the ball outward. (    )In addition to the centripetal force shown in the figure, there must also be a force radially inward from the string to cause circular motion. (     )In addition to the centripetal force shown in the figure, there must also be a force tangent to the motion of the ball. (     ) The centripetal force inward and the centrifugal force outward must balance each other. (     )Only the centripetal force shown in the figure is required.

Explanation / Answer

When an object is moving in a circle

Only centripetal force is required to accelerate the object to keep it moving in a circular path

Centrifugal force is pseudo force acting on the object in a non inertial frame of reference

so the correct answer is the last option

i.e. Only the centripetal force shown in the figure is required.

centripetal force = M*v^2 /R

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