Advertisements
Advertisements
Question
Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force.
Solution
Mass of the object, m = 20 kg
Total work done by the force = Change in the object's kinetic energy
= `1/2 mv^2 - 1/2 m u^2`
= `1/2 m (v^2 - u^2)`
u = 5ms−1, u = 2ms−1, m = 20 kg
= 4 × 5
= 20
Hence, work done = `1/2m (v^2 - u^2)`
= `1/2 xx 20 [(2)^2 - (5)^2]`
= 10 × (−21)
= −210 J
The force will do work equivalent to 210 J. Here, the direction of force is opposite the direction of motion.
APPEARS IN
RELATED QUESTIONS
Write an expression for the kinetic energy of an object.
The kinetic energy of an object of mass m moving with a velocity of 5 m s−1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
A cyclist doubles his speed. How will his kinetic energy change: increase, decrease or remain same?
A body falls freely under gravity from rest. Name the kind of energy it will possess on reaching the ground.
Write an expression for the kinetic energy of a body of mass m moving with a velocity v.
How does the kinetic energy of a moving body depend on its (i) speed, and (ii) mass?
A man drops a 10 kg rock from the top of a 5 m ladder. What is its speed just before it hits the ground? What is its kinetic energy when it reaches the ground? (g = 10 m/s2)
What do you understand by the kinetic energy of a body?
A car of mass 120 kg is moving at a speed 18 km/h and it accelerates to attain a speed of 54 km/h in 5 seconds. Calculate:
- the work done by the engine.
- the power of the engine.
