NCERT Class 9 Science Solutions: Chapter 8 – Motion Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 4:

Q. What is the quantity which is measured by the area occupied below the velocity-time graph?

Answer:

Velocity-Time Graph of a Uniformly Moving Body

The graph shows the Velocity-time graph of a uniformly moving body.

Let the velocity of the body at time (t) be v.

Area of the shaded region

Where,

Length

Breath

Area

We know,

From equations (i) and (ii) ,

Area Distance

Hence, the area occupied below the velocity-time graph measures the distance covered by the body.

Question 1:

Q. A bus starting from rest moves with a uniform acceleration of m for 2 minutes. Find (a) the speed acquired, (b) the distance travelled.

Answer:

(a)

(a) Initial speed of the bus, (Since the bus is initially at rest)

Acceleration,

Time taken, minutes

Let v be the final speed acquired by the bus.

(b) According to the third equation of motion:

Where, s is the distance covered by the bus

Speed acquired by the bus is 12 m/s.

Distance travelled by the bus is 720m.

Question 2:

Q. A train is travelling at a speed of 90 km . Brakes are applied so as to produce uniform acceleration of m . Find how far the train will go before it is brought to rest.

Answer:

Initial speed of the train,

Final speed of the train, (finally the train comes to rest)

Acceleration m

According to third equation of motion:

as

Where, s is the distance covered by the train

The train will cover a distance of 625 m before it comes to rest.

Question 3:

Q. A trolley, while going down an inclined plane, has an acceleration of 2 cm . what will be its velocity 3 s after the start?

Answer:

Initial velocity of the trolley, (since the trolley was initially at rest)

Acceleration, cm

According to the first equation of motion:

Where, v is the velocity of the trolley after 3 s from start is 0.06 m/s or 6 cm/s.

Q_3_Image_Showing_Velocity_Of_Trolley

Question 4:

Q. A racing car has a uniform acceleration of 4 m . What distance will it cover in 10 s after start?

Answer:

Initial velocity of the racing car, (since the racing car is initially at rest)

Acceleration,

Time taken,

According to the second equation of motion:

Where, s is the distance covered by the racing car

Hence, the distance covered by the racing car after 10 s from start is 200 m.

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