Question

A car is moving in a straight line with speed 18 kmh. It is stopped in 5 s by applying the brakes.

Find : (i) the speed of car in m s-, (ii) the retardation and (iii) the speed of car after 2 s of applying the brakes.





please type the complete solution​

Answer 1

Given

Initial speed of car = 18 km/h

Car stopped in 5 s by applying brakes.

To Find

i) Speed of car in m/s

ii) The retardation of car

iii) Speed of car after 2 s of applying brakes.

Solution

i) Initial speed of car = 18 km/h

Converting it into m/s

⇒ Speed of car = 18 km/h

⇒ Speed of car = 18 × (5/18) m/s

⇒ Speed of car = 5 m/s

So, speed of car in m/s = 5 m/s (i)

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ii) Here, initial speed of car = 5 m/s

As the car stops, final speed of car = 0 m/s

Time taken to stop = 5 s

We know that,

⇒ a = (v - u)/t

⇒ a = (0 - 5)/5

⇒ a = -5/5

⇒ a = -1 m/s²

[Negative sign shows retardation ]

So, retardation of car = 1 m/s² (ii)

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iii) Initial speed = 5 m/s

Time taken = 2 s

Acceleration of car = -1 m/s²

We know that,

⇒ v = u + at

⇒ v = 5 + (-1) × 2

⇒ v = 5 - 2

⇒ v = 3 m/s

So, speed of car after 2 s = 3 m/s (iii)

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