Question

Which of the following is true for a system comprising of two bodies in contact exerting frictional force on each other

• A. total work done by the static friction on whole system is always zero
• B. work done by the static friction is always negative
• C. work done by the kinetic friction on the body is always negative
• D. total work done by internal kinetic friction on whose system is always negative

Answer 1

The correct option is A total work done by the static friction on whole system is always zero

For a system comprising of two bodies in contact exerting frictional force on each other. some point to remember

1) As external force work done by the static friction is always zero.

2) As an internal force, total work done by the static friction on whole system is always zero

3) Work done by the kinetic friction on an object is always negative because the displacement is always opposite to the frictional force. Although some cases work done can be both positive and negative.

The correct option is A.