Question

A body of mass $m$ is projected with initial speed $u$ at an angle $\theta$ with the horizontal. The change in momentum of body after time $t$ is

• A. $mu\sin \theta$
• B. $2mu\sin \theta$
• C. $mgt$
• D. Zero

Answer 1

The correct option is C $mgt$

• In motion under $gravity$ the horizontal velocity remain $constant$ so $only$ the change in vertical velocity is to be taken into account.

after time t the vertical velocity is $v=usin\theta -gt$

where $usin\theta$ is initial vertical velocity so $change$ in velocity is $-gt$ taking $modulus$ it become $gt$

so change in momentum will be $\text{mass multiplied by gt}$

so answer is $mgt$ means Option C.