Question

A ball is rolled off along the edge of table (horizontal) with velocity $3m/s$. It hits the ground after time $0.4s$. Which one of the following is wrong ?

• A. The height of the table is $0.8m$
• B. It hits the ground at an angle of ${60}^0$ with the vertical.
• C. It covers a horizontal distance $1.2m$ from the table.
• D. It hits the ground with vertical velocity $4m/s$.

Answer 1

The correct option is B It hits the ground at an angle of ${60}^0$ with the vertical.

Consider motion in vertical direction

given, $u_y=0,t=0.4s,u_x=3m/s$

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, $v_x=u_x=3m/s$

$tan\theta =\frac{v_x}{v_y}=3/4$

horizontal distance, $=u_{x}t=1.2m$

resultant final velocity, $v=\sqrt{v_x^2+v_y^2}=5m/s$

Hence answer is option (c)