Momentum
Beginner
Theorem of Momentum
Source: High school physics (Chinese)
Problem Sets:
momentum - 1111
Problem
As shown in Figure, a ball with mass $m=1$ kg strikes a horizontal steel plate at a speed of $v=10$ m/s and an angle of $60^\circ$ with the horizontal. It rebounds with the same speed and angle.
Find the magnitude and direction of the change in the ball's momentum.
P0582-problem-1
$|\Delta\vec{p}| = 17.3$ kg·m/s, vertically upward.
The initial and final velocity components are $v_x = v \cos 60^\circ$ and $v_y = \pm v \sin 60^\circ$. The horizontal momentum component does not change. The change in momentum is only in the vertical direction.
$$ \Delta p = p_{fy} - p_{iy} = m(v \sin 60^\circ) - m(-v \sin 60^\circ) = 2mv \sin 60^\circ $$The direction is vertically upward, perpendicular to the plate.