Question

A stone is dropped from rest from the roof of a building 150 meters high. (a) What is the velocity of the stone after 2 sec? (b) How far is the stone from the ground after 2 sec? (c) What is its velocity the moment it strikes the ground?

Answer 1

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ANSWER:

• a) velocity of the stone after 2 sec = 19.6 m/s

• b) How far is the stone from the ground after 2 s = 140.4

• c) velocity of the stone at the moment it strikes the ground = 0

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GIVEN:

• A stone is dropped from rest.

• Building is 150 meters high.

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TO FIND:

• a) velocity of the stone after 2 sec

• b) How far is the stone from the ground after 2 sec.

• c) velocity of the stone at the moment it strikes the ground.

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EXPLANATION:

a) velocity of the stone after 2 sec:

$\boxed {\large{ \bold{{v = u + at}}}}$

u = 0

a = 9.8 m/s²

t = 2 s

v = 0 + 9.8(2)

v = 19.6 m/s

velocity of the stone after 2 sec = 19.6 m/s

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b)How far is the stone from the ground after 2 sec:

$\boxed {\large{ \bold{{s = ut + \frac{1}{2} a {t}^{2} }}}}$

u = 0

t = 2 s

a = 9.8 m/s²

s = 0(t) + 1/2(9.8)2²

s = 9.8 (2)

s = 19.6 m

The distance from the ground = Total height - distance travelled in 2s

The distance from the ground = 160 - 19.6

The distance from the ground = 140.4

How far is the stone from the ground after 2 s = 140.4

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c) velocity of the stone at the moment it strikes the ground.

The velocity of the stone when it strikes the ground will be zero, because after striking the ground it will come to rest.

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