Question

mass 0.3kg is moving on the ground at speed 4m/s towards ball B which is at rest on the ground and has mass of 0.8kg. When A collides with B the ball remains in contact for 0.2 sec after the collision B moves forward with a velocity of 1.8m/s find the average force of A and B during collision and explain above the total kinetic energy of the system before and after the collision.

Answer 1

Initial momentum of A = .3*4 = 1.2 kg m/s

Final momentum of B = .8*1.8 = 1.44 kg m/s

change of momentum of B = 1.44-0 = 1.44
so
Force on B = change in momentum/time
= 1.44 kg m/s / .2 s = 7.2 Newtons

Now final velocity of A from conservation of momentum
1.2 = 1.44 + .3 Va
so
Va = - 0.8 m/s
so now the energy stuff
initial Ke = (1/2)(0.3)(16)
Final Ke = (1/2)(.3)(-.8)^2 + (1/2)(.8)(1.8)^2
I hope the final is less than the initial