A stone is thrown upward at an angle of 20◦ above the horizontal. Its maximum height during the trajectory is 41 m. The acceleration of gravity is 9.81 m/s 2. What was the stone's initial speed? Answer in units of m/s.

Stone's initial speed = 82.93 m/s

Explanation:

Consider the vertical motion of stone.

We have equation of motion v² = u² + 2as

At maximum height

Final velocity, v = 0 m/s

Acceleration, a = - 9.81 m/s²

Displacement, s = 41 m

Substituting

v² = u² + 2as

0² = u² + 2 x - 9.81 x 41

u = 28.36 m/s

We know that initial velocity in vertical motion is sin component of original initial speed.

That is

Initial speed x sin 20 = 28.36

Initial speed = 82.93 m/s

Stone's initial speed = 82.93 m/s