Question

please help physics class 11 and spammers will be reported ​

Answer 1

Explanation:

The first stone falls 20m without any initial velocity. The only acceleration is a constant g = 10m/s². We can use the equations of motion to find the time taken for the stone to fall, using the equation -

s = u*t + 1/2*a*t²

Here, s = 20m, u = 0 m/s, and a = 10 m/s².

Thus, 20 = 0 + 1/2*10*t²

20 = 5*t²

4 = t²

t = 2s (as t = -2s isn't possible)

The second stone was dropped 1s later, and it reached the ground simultaneously. So, it travelled 20m in 2-1 = 1s. Let's assume it's initial velocity as u m/s. Using the same equation of motion,

s = u*t + 1/2*a*t²

20 = u*1 + 1/2*10*1²

20 = u + 5

u = 15 m/s.

Thus, the second stone was thrown with a speed of 15 m/s.

Hence, option B is the right answer.