Question

when brakes are applied to a car moving with a velocity of 54 km^-1 it comes to rest within 2 metre. calculate the frictional resistance if mass of the car is 150 kg​

Answer 1

Explanation:

With the given data, one can easily calculate the value of retardation of the car by using the equation of motion:

v^2 - u^2 = 2as

where

'v' is the final velocity of the car which is 0 (because the car comes to a halt after applying the brakes)

'u' is the initial velocity of the car which is

10 m/s

'a' is the retardation which is to be determined

's' is the distance the car treads after applying the brakes and coming to a halt, which is 20 m

Thus, the retardation comes out to be

2.5 m/s^2

Now, we know that

Force = Mass x Acceleration

Assuming the mass of the car to be M kg, the stopping force comes out to be 2.5M Newtons

Now if this force were to stop the same car travelling at 30 m/s, it would produce the same retardation as it did earlier, because the mass of the car is unchanged.

Now, u=30 m/s instead of 10 m/s

Using the same equation

v^2 - u^2 = 2as

The stopping distance 's' comes out to be

180 m

The lesson to learn here is that if your car stops in 80 feet doing 80 km/hr does not mean it will stop in 100 feet doing doing 100 km/hr. This is the reason why road authorities hesitate to increase speed limits even by humble amounts!

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Answer 2

Answer:

Acceleration due to friction (retardation) (a) = - μg=−0.9×10=−9m/s

2

Final velocity, v=0m/s

Initial velocity, u=20m/s

Applying formula: v

2

=u

2

+2as

Where s is the distance traveled by car before it come to rest.

⇒0

2

=20

2

+2(−9)s

⇒18s=400

⇒s=22.2 m

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