CBSE Class 11-science Answered

Let us take upward direction as positive and downward direction as negative.

1. u = 9.8m/s, h = -39.2m,

use s= ut+1/2at^2 and solve for t. You will get two values for t. Now I want you to think and tell me which of these two is the value that we are looking for.

2. When the stone passes through its point of projection, the distance covered by it is zero. So put h = 0; hope you got this point. Draw a diagram on which you draw a building, a stone and then its position when it is at its point of projection.

next use the equation s=ut+1/2at^2 to find t.

3. to find the velocity with which it strikes the ground use v^2 = u^2 +2as and put the values of u, a and s with appropriate signs. once again draw a diagram where you have clearly indicated all values.