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Question
car moving at 40 km/hr is to be stopped by applying brakes in the next 4 m. If the car weighs 2000 kg, what average force must be applied to stop it?
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Solution
Given:
Initial speed of the car, u = 40 km/hr
\[= \frac{4000}{3600} = 11 . 11 m/s\]
Final speed of the car, v = 0
Mass of the car, m = 2000 kg
Distance to be travelled by the car before coming to rest, s = 4m
Acceleration,
\[a = \frac{v^2 - u^2}{2s}\]
\[\Rightarrow a = \frac{0^2 - \left( 11 . 11 \right)^2}{2 \times 4} = \frac{- 123 . 43}{8} = - 15 . 42 m/ s^2\]
∴ Average force to be applied to stop the car, F = ma
⇒ F = 2000 × 15.42 ≈ 3.1 × 104 N
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