Question

A body of mass $5kg$ starts from the origin with an initial velocity $\overrightarrow{u}=(30\hat{i}+40\hat{j})m{s}^{-1}$. If a constant force $\overrightarrow{F}=-(\hat{i}+5\hat{j})N$ acts on the body, the time in which the y-component of the velocity becomes zero is

• A. $5s$
• B. $20s$
• C. $40s$
• D. $80s$

Answer 1

The correct option is C $40s$

Here, mass of the body , $m=5kg$; y-component of initial velocity, $u_y=40m/s$ and y-component of the force, $F_y=-5N$

Using $F=ma$, $a_y=\frac{F_y}{m}=\frac{-5}{5}=-1m/s^2$

Using formula, $v=u+at$

$v_y=u_y+a_{y}t$

So, $0=40-t$

$\therefore t=40$ sec