A stone is thrown from the top of a cliff 70m high at an angle of 20o from the bottom

of the cliff. Find the initial speed of the stone and the direction in which it is moving

when it hits the sea 2 seconds after projection.​

Probably 27 m/s downward at 20° from vertical

Explanation:

I will ASSUME that you mean projection at an angle of 20° above the horizontal.

The general equation

s = s₀ + v₀t + ½at²

in the vertical plane, becomes

0 = 70 + (v₀sin20)(2.0) + ½(-9.8)(2.0²)

-(v₀sin20)(2.0) = 70 - 19.6

v₀ = -73.69 m/s

as a negative velocity does not make sense, I suspect that the initial assumption is incorrect.

If I ASSUME that you mean projection angle is 20° below the horizontal.

0 = 70 + (v₀sin-20)(2.0) + ½(-9.8)(2.0²)

v₀ = 73.69 m/s which, while positive, seems an improbable velocity for a human throw.

If I ASSUME that you mean projection angle is 20° from the vertical.

0 = 70 + (v₀cos20)(2.0) + ½(-9.8)(2.0²)

v₀ = -26.81727

which is downward at about 27 m/s, a fairly reasonable answer for a human thrower.