Question

Calculate the work required to be done to stop a car of 1300 Kg moving at a speed of 54Km/h.

Answer 1

see attachment....I hope it will helps

Answer 2

Mass , m = 1300 kg
Velocity = 54 km/ hr

For converting km/hr to m/s , we usually multiply it with $\frac{5}{18}$ .
Initial velocity , u = 54  × $\frac{5}{18}$
                            = 15 $m/s$

Final velocity , v = 0 m /s

According to Work energy theorem , Work done is equal to change in Kinetic energy.

Kinetic energy is the energy possessed by a body by virtue of its motion .

Kinetic energy = $\frac{1}{2} mv ^{2}$ - $\frac{1}{2} m u^{2}$ 
                        = $\frac{1}{2}$ × 1300 × 0 - $\frac{1}{2}$ × 1300 × 15 ²

                        =  0 - $\frac{1}{2}$ × 1300 × 15 × 15
                        =  - 146250 Joules.

The work done here is negative.This is because force and displacement are in the opposite direction.....