Question

A car moving with a velocity 54 km/h on a straight
road stops on applying brakes after covering a
distance of 20 m. Compute the acceleration of the car.

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Answer 1

Intial velocity of car, u = 54 km/h = 54 × 5/18 m/s

u = 15 m/s

Car stops on applying brakes 20m

Displacement is covered by car ,S = 20m

finally car stops ∴ final velocity of car , v = 0

Now, use formula

V² = u² + 2aS , here a is Acceleration

⇒ 0 = (15)² + 2 × a × 20

⇒ -225 = 40a

⇒ a = -5.625 m/s² [ here negative sign shows that acceleration is opposite direction of motion of car ]

Hence, magnitude of acceleration = 5.625 m/s²

Answer 2

velocity (intial)= 15m/s

velocity(final) = 0m/s

distance =20m

acceleration=?

we know that,

v²-u²=2as

(0)²-(15)²=2a(20)

-225= 40a

a= -5.625m/s²

acceleration is 5.625 as the( - ) is opposite direction of motion.