Neeraj reaches school in a car at an average speed of 20 km h . While returning; his speed becomes 30 km h due to lesser crowd. What is the average speed of Neeraj's car for the whole journey?

Let us assume that the distance between School and Neeraj's starting point (say home) be X km . It is given that, Speed of car during the journey to school, v 1 = 20 km h Speed of car during return journey, v 2 = 30 km h Let t 1 and t 2 be the time taken for the journey to school and for return journey respectively. We know that, Speed = Distance Time ⇒ Time = Distance Speed Therefore, t 1 = X 20 s , t 2 = X 30 s The average speed of the car, v a v g = Total distance covered Total time taken = X + X X 20 + X 30 = 2 X 50 X 600 = 1200 50 = 24 km h Therefore, the average speed of the car is 24 km h

A ball is dropped from the top of a 20 m high tower. If its velocity is increasing with an acceleration of 10 m s 2 then at what speed will the ball hit the ground? How much time will it take to hit the ground?

Given, The distance travelled by the ball, s = 20 m The acceleration of the ball, a = 10 m s 2 Let u , v and t represents the initial velocity, final velocity and time of flight respectively. We have, u = 0 Applying third equation of motion, v 2 = u 2 + 2 a s = 0 + 2 × 10 × 20 = 400 m 2 s 2 Therefore, v = 400 = 20 m s Now applying first equation of motion. v = u + a t t = v - u a t = 20 - 0 10 = 2 s Therefore, the ball will hit the ground 2 s after the drop.

E M B I B E

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 5

MEDIUM

9th Chhattisgarh Board

IMPORTANT

Earn 100

The displacement-time graph for an object is given below. What result can you find out for its velocity?

Important Questions on Motion

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9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 6

The position-time graph for a given object is a straight line parallel to its time axis. What can you say about its motion?

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9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 7

Define uniform motion and a non-uniform motion also state two example of each.

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9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 8

Write all the three equations of motion and explain the symbols used in them.

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9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 9

An athlete covers one round of a circular track of

7 m

radius is

44 s

. How much distance(in metre) will it cover in

1

minute? (Fill up to one decimal place)

HARD

9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 10

Using the graphical method derive the second equation of motion

s = u t + \frac{1}{2} a t^{2}

HARD

9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 11

Neeraj reaches school in a car at an average speed of

20 \frac{km}{h}

. While returning; his speed becomes

30 \frac{km}{h}

due to lesser crowd. What is the average speed of Neeraj's car for the whole journey?

HARD

9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 12

A ball is dropped from the top of a

20 m

high tower. If its velocity is increasing with an acceleration of

10 \frac{m}{s^{2}}

then at what speed will the ball hit the ground? How much time will it take to hit the ground?

HARD

9th Chhattisgarh Board

IMPORTANT

Science (Theory & Practical) Class-9>Chapter 4 - Motion>Exercise>Q 13

A car is moving on a straight road at a uniform acceleration. The velocity of the car at different times is given below. Draw its velocity-time graph and calculate its acceleration and also find out the distance covered by it in $30$ seconds.