✔ 最佳答案
Momentum is a vector quantity. You need to use vector substraction in calculating the change of linear momentum.
Since change of momentum = final momentum - initial momentum
the momentum vectors thus forms a right-angle triangle with the hypotenus as the "momentum difference".
Thus, change of momentum = square-root[(2000x0.5)^2 + (2000x0.4)^2] kg.m/s
= 1281 kg.m/s
Let a be angle between the momentum change and the final momentum
hence, tan(a) = 0.5/0.4
a = 51.34 degrees.