# CBSE 9th Physics | Motion NCERT Problems with Solutions- Part 2

## Motion NCERT Problems with Solutions- Part 2

Motion is a very important topic of Physics. Here are Motion NCERT Problems with Solutions for your practice

### Problem 2. Fig. shows the distance-time graph of three objects A, B and C. Study the graph and answer the following questions:

#### How far has B traveled by the time it passes C?

(ii) No, all three do not meet at any point on the road,

(iii) When B passes A at point N (at 1.2 hours), C is at a distance of approximately 8 km from

the origin O.

(iv) B passes C at 0.7 hours. During this time B covers distance of 6 km.

### Problem 4. The speed-time graph for a car is shown is Fig.

#### (b) Which part of the graph represents uniform motion of the car?

(a) On horizontal axis, 5 small divisions = 2 s On vertical axis, 3 small divisions = 2 m/s

Area of 15 small squares

= 2 s x 2 m/s = 4m

Area of 1 small square =4/15m

Total area under the speed-time graph from time 0 to 4 s

= 57 small squares + 1/2 x 6 small squares

= 60 small square

Distance traveled by the car in first 4 seconds

= Area under the speed-time graph from 0 to 4 s

= 60 small squares

= 60 x 4/15 m

= 16 meter.

(b) After 6 s, the car has a uniform motion for straight part of graph BC.

### Problem 5. State which of the following situations are possible and give an example for each of these:

#### (b) an object moving in a certain direction with an acceleration in the perpendicular direction.

(a) Yes, a body can have acceleration even if its velocity is zero. When a body is thrown

up, at highest point its velocity is zero but it has acceleration equal to acceleration due to gravity.

(b) Yes, when an object moves on a circular path, it has centripetal acceleration which is perpendicular to displacement.

# CBSE 9th Physics | Motion – Solved Problems

## Motion – Solved Problems

### Problem 1. A car covers the 1st half of the distance between two places at a speed of 40 km/hr and the 2nd half at 60 km/hr what is the average speed of the car ?

Solution.

Suppose the total distance covered is S. Then time taken to cover first’s distance with speed

40 km/hr.

### Problem 2. An object moving to the right has a decrease in velocity from 5.0 m/s to 1.0 m/s in 2.0 s. What is the average acceleration ? What does your result mean ?

Solution.

Given v0 = + 5.0 m/s, v = + 1.0 m/s, t = 2.0 s

Find

According to the definition of average acceleration,

The negative sign means the acceleration is opposite to velocity (deceleration). The result means that the object decreases its velocity by 2.0 m/s every s or 2.0 m/s2.

### Problem 3. The table below shows the distance in cm, travelled by the objects A, B and C during each second.

#### (iii) Which object is moving with irregular acceleration ?

Solution

The object A is moving with constant speed. The reason is that it covers equal distance=20cm. in each second,

The object C is moving with a constant acceleration. The reason is that for the object C, the distance covered increases by the same amount in each second. It can further be verified by drawing graph between S (total distance covered) and t2 (square of time taken). The graph will be a straight line.

 t2 1 4 9 16 25 s 20 80 180 320 500

The object B is moving with irregular acceleration.

### Question 4. An automobile accelerates uniformly from rest to 25 m/s while traveling 100m. What is the acceleration of the automobile ?

Solution.

Given: v0 = 0 (rest), v = 25m/s, x = 100m. Find a.

Since v2 = v02 + 2ax,

Since a is positive, it is in the direction of the velocity or motion.

Solution.

Solution.

Solution.

Solution. (i)

Solution (ii)

### Problem 9. The graph represents the velocity of a particle as a function of time.

#### (e) What is the displacement for the 8.0 s interval ?

Solution. (a)

Solution (b)

The slope of the line is zero and a = 0.

Solution (c)

Solution (d)

Solution (e)