Subject: Error in the working.
Author:
Posted on: 2013-04-11 22:11:00 UTC
CoM says that (duh) momentum is conserved - it doesn't say that a 1kg ball can stop a 10kg ball dead in its tracks. Balls of equal mass exchange velocities in that way; unequal masses don't.
Running via wiki, I find a pair of equations (under 'Elastic collisions') allowing you to determine the final velocity, v(1,2), from the initial velocities u(1,2) and the masses m(1,2). For your 10kg mass, the equation reads:
v1 = ((m1-m2)/(m1+m2))*u1 + ((2*m2)/(m1+m2))*u2
Given that u2 (initial velocity of the smaller ball) = 0, and inputting the other figures, that gives:
v1 = (9/11) * 1 = ~0.82 m/s.
k.e. = 1/2 m1*v1^2 = 3.35 J.
The equation for m2 is the same, except with the subscripts flipped. Running the numbers gives us:
v2 = (20/11) * 1 = ~ 1.82 m/s
k.e. = 1.65 J.
And, of course,
3.35 + 1.65 = 5 J.
Does that answer your question?
(Short version: a bowling ball rolled at a ping-pong ball won't fire the ping-pong ball off into orbit)
hS