Question

If a rock is thrown 0.8 meters into the air, How fast was it thrown

Answer 1

Answer:

Speed, s = 3.95 m/s

Explanation:

It is given that, a rock is thrown 0.8 meters into the air. We have to find the velocity with which it is thrown.  

Using conservation of mechanical energy as :

$K_i+P_i=K_f+P_f$

Initial potential energy at the ground is 0 and at maximum height the final kinetic energy is 0.

So,

$\dfrac{1}{2}mv^2=mgh$

$v=\sqrt{2gh}$

putting g = 9.8 m/s² and h = 0.8 m

$v=\sqrt{2\times 9.8\times 0.8}$    

v = 3.95 m/s

Hence, it was thrown with a speed of 3.95 m/s

Answer 2

V=0 m/s, u=?, a = 9.8 m/s² and s = 0.8 m
u²=2×9.8×0.8=15.68
u=3.959 ≈ 3.96 m/s