Mark out the correct statement(s).

Options

A. Total work done by internal forces on a system is always zero
B. Total work done by internal forces on a system may sometimes be zero
C. Total work done by friction can never be zero
D. Total work done by friction is always zero

Answer

B

Explanation

(b) Work done by friction mayt be positive, negative and zero. Work done by conservative, internal forces may be zero in a round trip but it is non-zero for non-conservative internal forces.