First slide

Law of conservation of momentum and it's applications

Question

An object of m kg with speed of v m/s strikes a wall at an angle $θ$ and rebounds at the same speed and same angle. The magnitude of the change in momentum of the object will be

Moderate

A

$2 m v \cos θ$
B

$2 m v \sin θ$
C

0
D

$2 m v$

Solution

$\begin{array}{l} {\vec{P}}_{1} = m v \sin θ \hat{i} - m v \cos θ \hat{j} \\ and {\vec{P}}_{2} = m v \sin θ \hat{i} + m v \cos θ \hat{j} \\ So change in momentum \\ \vec{Δ P} = {\vec{P}}_{2} - {\vec{P}}_{1} = 2 m v \cos θ \hat{j}, | Δ \vec{P} | = 2 m v \cos θ \end{array}$

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