Question

The work done in increasing the speed of a car of mass 800 Kg from 10 m/s to 20 m/s is
a. 800 J
b. 200 J
c. 120000 J d. 1000 J

Answer 1

Answer:

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Answer 2

Answer:

Mass of a car = 800 kg

v₁ = 10 m/s  v₂ = 20 m/s

The kinetic energy of the car when its speed is 10 m/s is given as:

K₁ = 1/2 m v₁²

K₁ = 1/2 (800) (10)²

K₁ = 4*10^4 J

The kinetic energy of the car when its speed is reduced to 20 m/s is given as:

K₂ = 1/2 m v₂²

K₂ = 1/2 (800) (20)²

K₂ = 16*10^4 J

So, the work done by the brake will be the difference of their kinetic energies.

Therefore,

K₂ - K₁ = -4*10^4 +  16*10^4

K₂ - K₁ =  12*10^4 J

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