7. A particle of mass m moving with velocity u makes an elastic one dimensional collision with a stationary particle of mass m. They are in contact for a very short time T. Their force of interaction increases from zero to F0 linearly in time T/2, and decreases linearly to zero in further time T/2. The magnitude of F0 is
(a) mu/T
(b) 2mu / T
(c) mu/ 2T
(d) None of these
ANS. b
(5)