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Motion In Straight Line

Question

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A stone falls from a cliff and travels 45m in last second before it reaches the ground. What is the height of cliff? (Given g = 10 m/s²)

Solution

Let, height of the cliff be 'h'.

Time taken by the stone to reach the ground = n

The distance travelled by particle in nth second is given by,
$S_{n t h} = u + \frac{a}{2} (2 n - 1)$

Here we have,

$Snth = 45 m, u = 0, a = 10 m / s^{2}$

$∴ 45 = 0 + \frac{10}{2} (2 n - 1)$

$\Rightarrow$ n = 5 s

i.e. Stone takes 5 s to reach the ground from top of cliff.

Now the height of cliff is,

$h = ut + \frac{1}{2} {gt}^{2} = 0 \times 5 + \frac{1}{2} \times 10 \times (5)^{2} = 125 m$

Some More Questions From Motion in Straight Line Chapter

What is the most essential thing to study the motion of a body?

Can a body be always at rest in some frame?

Can a body be in motion in the frame associated with the body itself?

When an object in motion can be considered as particle or point object?

Can you think of physical phenomena involving the moon in which moon cannot be treated as particle?

A train is crossing the bridge. Can it be taken as a particle?

Can a train be taken a particle? Give an example in support of your answer.

A particle is moving along curved line in space. Is the motion one dimensional?

State which of the following are examples of one, two or three dimensional motion:

(a) A kite flying in the sky.

(b) The earth revolving around the sun.

(c) A train moving along the equator of the earth in clockwise direction.

(d) Accelerated motion of a particle in a straight line.

Define distance.

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