Question

A stone is dropped from the top of a 40 m high tower. Calculate its speed after 2 s. Also find the speed with which the stone strikes the ground.​

Answer 1

$\huge\bf{\underline{\underline{\sf{\red{Answer:}}}}}$

• The speed of the stone after 2s is 19.6 m/s

• The speed with which the stone strikes the ground is 28 m/s

$\huge\bf{\underline{\underline{\sf{\purple{Explanation:}}}}}$

✤ Given :

• Height = 40m
• Time = 2 sec

✤ To Find :

• It's speed after 2s.
• The speed with which the stone strikes the ground.

✤ Solution :

Formula used :

$➤ \: \: \large{\boxed{\sf{\pink{v=u+at}}}}$

where, u = 0 and a = g(acceleration due to gravity)

Substituting the values, we get,

$\mapsto{\sf{v = 0+9.8 \times 2}}$

$\mapsto{\sf{v = 19.6m/s}}$

The speed of the stone after 2s is 19.6 m/s.

After that, we have to find the stone strikes the ground,

Formula used :

$➤ \: \: \large{\boxed{\sf{\pink{v^{2}=u^{2}+2gs}}}}$

Substituting the values, we get,

$\mapsto\displaystyle{\sf{v^{2} = 0+2 \times 9.8 \times 40}}$

$\mapsto\displaystyle{\sf{v^{2}=784}}$

$\mapsto\displaystyle{\sf{v^{2}=784}}$

$\mapsto\displaystyle{\sf{v=\sqrt{784}}}$

$\mapsto\displaystyle{\sf{v=28m/s}}$

Therefore, the speed with which the stone strikes the ground is 28m/s.

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