Question

A dark blue ball moving with 55 m/s strikes a light red stationary ball of identical mass. After the collision the blue ball moves at 45 m/s, at an angle ? = 20? with respect to the original line of motion. (a) Find the velocity of the red ball after the collision, and nd the an- gle ?. (b) Is the collision elastic or in- elastic? - you must show a calculation to get marks for this question. (c) (1 mark) Does it make sense to have more total kinetic energy after the col- lision than before collision?

Answer 1

Assuming mass is same

let velocity of red ball is v m/s at angle theta below line of motion

conserving momentum in line of motion

m*55=m*45*cos(20)+m*v*cos(theta)

vcos(theta)=12.714

conserving momentum perpendicular to line of motion

m*45sin(20)=mvsin(theta)

vsin(theta)=15.39

we got v=19.96 m/s

theta=50.44 degree below line of motion

(b) initial kinetic energy=0.5m*55^2=1512.5m

final kinetic energy=1211.7m

As kinetic energy is not conserved ,it is inelastic collision

(c) No ,Energy will be less after collison . It does not make sense to have more total kinetic energy after the col- lision than before collision