PHYSICS MC CE LEVEL...

The direction of motion of the two carts and the direction in which Jack jumps are perpendicular to each other. Hence, they have no influence on one another.
唔係應該
mu=(m+n)v <--- wrong, you cannot write (m+n)v because the velocity of the cart and the velocity of Jack are NOT in the same direction.
The correct equation is: mu = mv, thus u = v




2009-04-05 13:12:51 補充：
Sorry...the equation, using your symbols, should be:
(m + n)u + mu = mv + (m+n)v for direction along motion of carts.
This reduces to (2m+n)u = (2m+n)v, thus u=v