Q. 64.5( 2 Votes )

# A car A is travelling on a straight level road with a uniform speed of 60 km/h. It is followed by another car B. Which is moving with a speed of 70 km/h. When the distance between them is 2.5 km, the car B is given a deceleration of 20 km/h^{2}. After how much time will B catch up with A?

A. 1 h

B.

C.

D.

Answer :

_{Distance covered by car A in time t is, s}_{1} = 60 t

For car B:

Using the second equation of motion: s = ut + at^{2}

where: s = distance covered = s_{2}

u = initial velocity = 70 km/h

a = acceleration = -20 km/h

t = time = t

s = ut + at^{2}

s_{2} = 70t + (-20) × t^{2}

s_{2} = 70t – 10 t^{2}

But it is given that s_{2} – s_{1} =2.5 km

70t – 10 t^{2} - 60 t = 2.5

10t - 10 t^{2} = 2.5

t – t^{2} = 0.25

t – t^{2} – 0.25 =0

t^{2} –t +0.25 =0

(t – 0.5)^{2} =0

t = 0.5 hr

Rate this question :

A cheetah starts from rest, and accelerates at 2 m/s^{2} for 10 seconds. Calculate :

(a) the final velocity

(b) the distance travelled.

Lakhmir Singh & Manjit Kaur - PhysicsObtain a relation for the distance travelled by an object moving with a uniform acceleration in the interval between 4^{th} and 5^{th} second.

A car accelerates from 6 ms^{–1} to 16 ms^{–1} in 10 sec. Calculate (a) the acceleration and (b) the distance covered by the car in that time.

A bus increases its speed from 36 km/h to 72 km/h in 10 seconds. Its acceleration is :

Lakhmir Singh & Manjit Kaur - PhysicsA bus is moving with a speed 72 km/h can be stopped by brakes after at least 10 m. What will be the minimum stopping distance, if the same bus is moving at a speed of 144 km/h?

All In One - ScienceDerive the formula: ,where the symbols have usual meanings.

Lakhmir Singh & Manjit Kaur - PhysicsThe speed-time graph of an ascending passenger lift is given alongside.

What is the acceleration of the lift :

(i) During the first two seconds?

(ii) between second and tenth second?

(iii) during the last two seconds?

Lakhmir Singh & Manjit Kaur - PhysicsA car is moving on a straight road with uniform acceleration. The speed of the car varies with time as follows :

Draw the speed-time graph by chooding a convenient scale. From this graph :

(i) Calculate the acceleration of the car.

(ii) Calculate the distance travelled by the car in 10 seconds.

Lakhmir Singh & Manjit Kaur - Physics