A body moves at a speed of $20 k m h^{- 1}$ for the first $2$ hours. After that, it moves at the speed of $30 k m h^{- 1}$ for the next 1 hour. What is the total distance travelled by the body?

60 k m

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70 k m

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80 k m

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90 k m

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Solution

The correct option is B $70 k m$
From definition of speed,
Distance = Speed $\times$ Time

The total distance will be the sum of the distances travelled in both the time intervals.

In the first part of motion,
$Speed = 20 k m h^{- 1}, Time = 2 s$
Distance travelled:
$D_{1} = 20 \times 2 = 40 k m$

In the second part of motion,
$Speed = 30 k m h^{- 1}, Time = 1 s$
Distance travelled:
$D_{2} = 30 \times 1 = 30 k m$

Hence, total distance: $D = D 1 + D 2 = 70 k m$

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A body moves at a speed of 20 km h−1 for the first 2 hours. After that, it moves at the speed of 30 km h−1 for the next 1 hour. What is the total distance travelled by the body?

A body moves at a speed of $20 k m h^{- 1}$ for the first $2$ hours. After that, it moves at the speed of $30 k m h^{- 1}$ for the next 1 hour. What is the total distance travelled by the body?