NCERT Class 9 Science Solutions: Chapter 8 – Motion Part 4

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Question 4:

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

Answer:

Image of 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)

Accelerationm

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.

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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