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. $2 m v \cos \theta$
• B. $2 m v \sin \theta$
• C. 0
• D. $2 m v$

Answer 1

Answer: (A)

$2 m v \cos \theta$

Answer 2

$\vec { P } _ { 1 } = m v \sin \theta \hat { i } - m v \cos \theta \hat { j }$ and

$\vec { P } _ { 2 } = m v \sin \theta \hat { i } + m v \cos \theta \hat { j }$

So change in momentum $\overrightarrow { \Delta P } = \vec { P } _ { 2 } - \vec { P } _ { 1 } = 2 m v \cos \theta \hat { j }$

$| \Delta \vec { P } | = 2 m v \cos \theta$