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 11

EASY

9th CBSE

IMPORTANT

Earn 100

State two differences between distance and displacement.

Important Questions on Motion

MEDIUM

9th CBSE

IMPORTANT

Core Science Physics For Class 9>Chapter 1 - Motion>EXERCISE>Q 12

The displacement of a moving object in a given interval of time is zero. Would the distance travelled by the object also be zero? Justify your answer.

MEDIUM

9th CBSE

IMPORTANT

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

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?

MEDIUM

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?

MEDIUM

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 .}

MEDIUM

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}

MEDIUM

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.

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