1.

A stone is dropped from the top of the tower. Its speed after it has fallen 20 m is (Take g = 10 ms-2)A. -10 ms-1B. 10 ms-1C. -20 ms-1D. 20 ms-1

Answer»

Here,

u = Initial velocity = 0

v = Final velocity

s = Distance travelled = 20 m

a = acceleration = g = 10 ms-2

Now, we know from the equations of motion that

v2 = u2 + 2as

v = \(\sqrt {u^2\,+\,2as}\)

v = \(\sqrt {0\,+\,2\,*\,10\,*\,20}\)

v = \(\sqrt {400}ms^{-1}\)

v = 20 ms-1

Hence, option D is correct.


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