Question

A ball of mass 2kg is moving with a speed of 10m/s along a flat surface. It collides with another ball of mass 3kg and comes to rest, what will be the speed of the second ball after collision?

(a) The above said situation is not possible

(b) 20m/s

(c) Zero

(d) 6.67m/s

I have been asked this question in semester exam.

The doubt is from Linear Momentum of a System of Particles in chapter System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Right option is (a) The above said situation is not possible

For explanation: When the balls collide, net external force on them is zero, so we can conserve momentum.                2*10 = 3*v                                                                                                                                                                                         ∴ v = 20/3 = 6.67m/s.

Note that the final kinetic energy is less than the initial kinetic energy, this is because the internal forces have done work during collision which gets converted into sound & heat energy.