Question

Calculate the amount of work required to stop a car of 1000kg moving with a speed of 72 km per hour

Answer 1

Here ,

Initial Velocity = u = 72 km/h = 20m/s

Final Velocity = v = 0 m/s

Mass of the body = m = 1000 kg

Now using the concept of Work Energy Theorem :

Work Done = ½mv²-½mu² = 0-½×1000×20 = 10000 N

The total work done is 10000 N.

Answer 2

Given:

• Initial speed = 72 km/hr
• Final velocity = 0
• Mass = 1000 Kg

To Find:

• The amount of work required to stop a car.

Solution:

The formula to find the work done to stop the car is given by,

Work done to stop = Initial Kinetic Energy  - Final Kinetic Energy

W = (1/2)×m×$u^2$ - (1/2)×m×$v^2$  → {equation 1}

We are converting 72 km/hr to m/s by dividing it by 3.6

⇒ 72/3.6 = 20 m/s

on substituting the values in equation 1 we get,

⇒ W = (1/2)×1000×(20×20) - (1/2)×1000×(0) {anything multiplied by zero is zero}

⇒ W = 500×400 - 0 {multiplying the terms}

⇒ W = 200000 = 2 × $10^5$ J

∴ The amount of work done to stop a car = 2×$10^5$