Question

A person is standing on a truck moving with $14.7m{s}^{-1}$ on a horizontal road. He throws a ball so that it returns to him when the truck has moved $58.8m$. Find the speed of the ball and angle of projection as seen by a man standing on the road.

• A. $22.5m{s}^{-1},{53}^{\circ }$
• B. $24.5m{s}^{-1},{53}^{\circ }$
• C. $19.6m{s}^{-1},vertical$
• D. none of these

Answer 1

Answer: (B)

$24.5m{s}^{-1},{53}^{\circ }$

Given, $R=58.8mV\cos \theta =14.7m/sTime=\frac{58.8}{14.7}=4s$
Now,
$4=\frac{2V\sin \theta }{g}V\sin \theta =2g$

Now,
$V^2{\cos }^2\theta +V^2{\sin }^2\theta ={\left(2g\right)}^2+{\left(14.7\right)}^2\Rightarrow V=24.5m/s\Rightarrow 24.5\cos \theta =14.7\Rightarrow \theta ={53}^{\circ }$