An object weighs 10 lbf at a location where the acceleration of gravity is 30. 0f t/s2. Deter-mine its mass, in lb.

C. 0 J

Explanation:

When an object moves in a circle, friction provides the centripetal force. Hence, it is acting towards the centre of the circle. The displacement of the object is tangential to the circle at the point of interest. Hence, the angle between the frictional force and the displacement is 90°.

Work done is given by

W = Fd cos θ

where F is the force, d is the displacement and θ is the angle between them.

W  = Fd cos 90° = 0 J

Hence, the work done by friction is 0 J.