A boy runs first 100 m with a uniform speed of 8 m s and the next 200 m with a uniform speed of 5 m s . Calculate the average speed of the boy.

Given, Distance travelled S 1 = 100 m , S 2 = 200 m Speed of travel v 1 = 8 m / s , v 2 = 5 m / s Assume time taken to cover the distance S 1 is t 1 and S 2 is t 2 . Speed = distance time ⇒ time = distance speed t 1 = S 1 v 1 = 100 8 = 12 . 5 s t 2 = S 2 v 2 = 200 5 = 40 s Total distance = S 1 + S 2 = 100 + 200 = 300 m Total time = t 1 + t 2 = 12 . 5 + 40 = 52 . 5 s Average speed = total distance total time Average Speed = 300 m 52 . 5 s = 5 . 71 m / s

A man travels a certain distance with a speed of 50 km h and returns back to the starting point with a speed of 40 km h . Calculate ( i ) average speed and ( ii ) average velocity of the whole journey.

Suppose the distance covered in one side journey is d . On board speed = 50 km hr Time = Distance Speed Time taken, t 1 = d 50 hr Returning speed = 40 km hr Time taken, t 2 = d 40 hr i Average speed = total distance total time v = d + d t 1 + t 2 v = 2 d d 50 + d 40 = 2 d d 40 + 50 40 × 50 v = 2 × 40 × 50 40 + 50 = 44 . 4 km h - 1 ( i i ) The Displacement is zero for the whole journey and the velocity is the displacement travelled in unit time. Hence, Average velocity = displacement total time v ' = 0 t 1 + t 2 = 0 v ' = zero

E M B I B E

Core Science Physics For Class 9>Chapter 1 - Motion>EXERCISE>Q 1

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9th CBSE

IMPORTANT

Earn 100

A body is moving along a circular path of radius $R$ . What will be the distance covered and the displacement of the body after half a revolution?

Important Questions on Motion

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9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>EXERCISE>Q 2

A person starts from his house and travels a circular distance of

15 km

around the walled city before returning back. What is the distance covered by person, and the displacement of the person?

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9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>Practice Problems>Q 1

A cyclist covers a distance of

50 m in 10 s

. Calculate the speed of the cyclist in

(i) \frac{m}{s}, (ii) \frac{km}{h .}

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9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>Practice Problems>Q 2

A train starts from rest and covers a distance of

450 m in 2 \min

. Calculate the speed of the train in

(i) \frac{m}{s}, (ii) \frac{km}{h}

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9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>Practice Problems>Q 1

An aeroplane flies

200 km

with a uniform speed of

300 \frac{km}{h}

and then another

200 km

with a uniform speed of

240 \frac{km}{h}

. Calculate the average speed of the aeroplane.

MEDIUM

9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>Practice Problems>Q 2

A boy runs first

100 m

with a uniform speed of

8 \frac{m}{s}

and the next

200 m

with a uniform speed of

5 \frac{m}{s}

. Calculate the average speed of the boy.

MEDIUM

9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>Practice Problems>Q 1

A man travels a certain distance with a speed of $50 \frac{km}{h}$ and returns back to the starting point with a speed of $40 \frac{km}{h}$ . Calculate $(i)$ average speed and $(ii)$ average velocity of the whole journey.