A ball is rolled off along the edge of the table (horizontal ) with velocity ` 4 ms^(-1)` .If hits the ground after time ` 0.4 s. Which one of the following statements is wrong ? ( g= 10 ms^(-2)).

Options

A. The height of table is ` 0.8` m`
B. It hits the ground at an angle of ` 60^2` with the vertical
C. It covers a horizontal distance ` 1. 6m` from the table
D. It hits the ground wigh vertical velocity ` 4 m//s`

Answer

B

Explanation

Height of table,
` h= 1/2 gt^2 = 1/2 xx 10 xx (0.4)^2 =0.8 m`
Horizontal distance coverd, ` u_x t= 4xx 0.4`
` = 1.6 m`
Vetical velocity on reaching ground ,
Vertical vellocity on reaching ground
` v_y =u_y =a_y t=0 + 10 xx 0.4 = 4 m//s`
Horizontal velocity on reaching ground,
` v_e = u-x =4 m//s`
If` theta` is the angle at which the ball hits he ground with the vertical, then
` tan theta = v_x/v_y = 4/4 = 1 ` or ` theta = 45^@`.
Thus, option (b) is wrong.