Question

A ball is rolled off along the edge of table (horizontal) with velocity $4m/s^{-1}$. It hits the ground after time $0.4s$. Which one of the following statement is wrong?
(Take $g=10m{s}^{-1}$)

• A. The height of the table is $0.8m$
• B. It hits the ground at angle of ${60}^o$ with the vertical
• C. It covers a horizontal distance $1.6m$ from the table
• D. It hits the ground with vertical velocity $4m{s}^{-1}$

Answer 1

The correct option is B It hits the ground at angle of ${60}^o$ with the vertical

Consider motion in vertical direction,

given, $u_y=0,t=0.4s,u_x=4m/s$

height, $h=u_y\times t+\frac{1}{2}g{t}^2=8m$

final vertical velocity, $v_y=u_y+gt=4m/s$

final horizontal velocity, $v_x=u_x=4m/s$

$tan\theta =\frac{v_x}{v_y}=\frac{4}{4}=1$
$\Rightarrow \theta ={45}^o$

horizontal distance, $=u_{x}t=4\times 0.4=1.6m$

So, all options are having right data except option$\left(B\right)$.
Hence, the correct option is $\left(B\right)$