Question

Calculate the amount of work done required to stop a car of 1000Kg moving with a speed of 72Km/hr

Answer 1

u = 72 km/h = 20 m/s
v = 0 km/h = 0 m/s.
By work energy theorem, we know
W = 1/2 mv^2 - 1/2 mu^2
W= 1/2 × 1000 × -400
= -200,000 J.

The minus sign indicates force and displacement are opposite to each other.

Answer 2

Given,  

m = 1000 kg

v = 72 km/h

To find,  

The Work done  

Solution,  

We can simply solve this numerical problem by using the subsequent process  

Now,  

Mass (m) = 1000 kg

Velocity (v) = 72 km/h

Converting from km/h to m/sec

⇒ 72×5/18 = 20m/s

Work done (W) = ?  

As we know that,

Work done = Change in Kinetic energy

i.e.   W = ½mv²

where,  

W = Work done, m = Mass, & v = Velocity

W = ½×1000kg×(20)²m/s²

W = 200,000 J

Therefore, the total work done is 2×10⁵ J