A girl of mass 2b Kg is initially at rest on ice with neglig

A girl of mass 2b Kg is initially at rest on ice with negligible friction She throws a 1 kg rock lo the right with a speed of 4 m/s (the tout mass of the girl. rock is 2t kg), What is the velocity of the girl after she throws the rock? Is kinetic energy conserved before and after she throws the rock? Discuss whether your answer to parts a and b are reasonable Give specific reasons why or why not you think so If you find the kinetic energy is conserved, is this what you would expect? If you find that kinetic energy increased, where did the energy come from? If you find that kinetic energy decreased where did the energy go?

Solution

a) assuming there is no friction.

so momentum of girl + rock system will not change.

applying momentum conservation,

26 x 0 = 25v + (1 x 4)

25v = - 4

v = - 0.16 m/s

so velocity of girl is 0.16 m./s to the left.

(b) before : Ki = (26 * 0^2 / 2) = 0

after Kf = 25 * 0.16^2/2 + 1 * 4^2 /2 = 8.32 J

(c) kinetic energy is increased because of work done by girl.

internal energy of girl converts into KE .