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Question
Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h?
Solution
Here, the mass of the car, m = 1500 kg
The initial velocity of the car, u = 60 km h-1
= `(60 xx 1000 m)/(60 xx 60 s)`
= `50/3 ms^-1`
The initial kinetic energy of the car,
`K.E_i = 1/2 "mu"^2`
= `1/2 (1500 kg) (50/3 ms^-1)^2`
= 208333.3 J
Final kinetic energy of the car,
`K.E_f = 1/2 mv^2`
= 0
Change in kinetic energy of the car
= K.Ef - K.Ei
= - 208333.3 J
The minus sign indicates the work is being done against the moving car.
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