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

• A. $2mv\cos\theta$
• B. $2mv\sin\theta$
• C. 0
• D. $2mv$

Answer 1

Answer: (A)

$2mv\cos\theta$

Answer 2

${\overset{\rightarrow}{P}}_{1} = mv\sin\theta\widehat{i} - mv\cos\theta\widehat{j}$ and

${\overset{\rightarrow}{P}}_{2} = mv\sin\theta\widehat{i} + mv\cos\theta\widehat{j}$

So change in momentum

$\overset{\rightarrow}{\Delta P} = {\overset{\rightarrow}{P}}_{2} - {\overset{\rightarrow}{P}}_{1} = 2mv\cos\theta\widehat{j},|\Delta\overset{\rightarrow}{P}| = 2mv\cos\theta$