Dodeef Dec 20, 2020

# a car is moving with a speed of 54 km /h comes to rest 2secondson applying brake ifthe mass of the car including the passengers is1000 kg what will be the force applied when brake is applied​

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• Force applied on Car on applying brakes = -7500 N
Given:-
• Car is moving with a speed of 54 km/h
• On applying brake Car comes to rest after 2 seconds
• Mass of the Car including passenger is 1000 kg
To find:-
• Force applied when the brake is applied, F =?
Formula required:-
• The first equation of motion

v = u + at

• The expression for newton's second law

F = ma

[ Where v = final velocity, u = initial velocity, a = acceleration, t = time, F = force, m = mass ]

Solution:-
• Initial velocity of Car, u = 54 km/h = 54×5/18  m/s = 15 m/s
• Final velocity of Car, v = 0
• time taken for coming to rest, t = 2 s
• Mass of Car with passenger, m = 1000 kg

Let, the acceleration of car on applying brake be 'a'

Using the first equation of motion

→ v = u + at

→ 0 = 15 + a × 2

→ -15 = 2 a

→ a = -7.5 m/s²

Let, the force acted on applying brake be 'F'

Using Newton's second law

→ F = ma

→ F = 1000 × -7.5

→ F = -7500 N

Therefore,

• A force of 7500 N (In the opposite direction of motion of Car) acted on applying brakes.
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Anastasiya
Dec 20, 2020