Question

A person throws two identical stones from the top of a 200-m
high cliff overlooking a lake. Stone 1 is thrown at an angle of
30^{o} above the horizontal with an initial speed of 40
m/s. Stone 2 is thrown at an angle of 30^{o} below the
horizontal with an initial speed of 40 m/s. Neglect air
resistance.

Which stone hits the water first?

Stone 1.

They hit at the same time.

Stone 2.

Which stone strikes the water with a greater speed?

Stone 1.

They strike with the same speed?

Stone 2.

Immediately before they strike the water, which stone has the greater acceleration?

Stone 1.

Stone 2.

They have the same acceleration.

Answer #1

(1) Since stone 1 will cover more distance compared to stone 2
and both had same initial velocity, **stone 2 will hit the
water first**.

(2) At the height of 200 m, both stones will have same speed :
40 m / s at 30^{o} below the horizontal. Both of the stones
will then travel same height 200 m under same acceleration : g =
acceleration due to gravity. Hence, **they will strike the
lake with same final speed**.

(3) Since both of the stones are falling under gravity, only
gravitational acceleration are acting on them. Hence, **they
have same acceleration** : g = 9.8 m / s^{2} .

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