Question

A stone is projected vertically upward at speed of 20 m/s and returned back to the initial position.what is the displacement then .what would be the speed of the stone when it returns to the starting point.(neglect air resistance).PLZ ANSWER THIS ..​

Answer 1

Explanation:

Let us take the point of projection as the origin of coordinate system. Let the up direction be taken as positive.

The initial velocity of the body = + 20 m/s

Acceleration due to gravity a= - 10 m/s²

Let the time taken to return to the ground be t second

Since the objects return to the ground, the displacement s= 0 m

Using the relation; s = u × t + ½ a t².

Substituting various values

0 = 20 t - ½ × 10× t²; ==> 20 t - 5 t² = 0;

5 t² - 20 t = 0; ==> 5 t (t - 4) = 0; ==> t= 0 sec. or t = 4 sec.

The body would be at the ground at the beginning ie at t =0 and again at t = 4s

Answer 2

The displacement will be 0 m and the speed will be 20 m/s