Here an object has mass of 20 kg which is changing it’s velocity from 5m/s to 2m/s. We know that work done is also equal to change in kinetic Energy.
work Done = Change in kinetic Energy
= Final kinetic Energy – Initial Kinetic Energy
= W = ½ m v² − ½ mu²
Mass (m) = 20 kg
Initial velocity (u) = 5 m s⁻¹
Final velocity (v) = 2 m s⁻¹
Formula:
Work done = Change in kinetic energy
W = ½ m v² − ½ mu²
W = ½ m (v² − u²)
W = ½ × 20 × (2² − 5²)
W = 10 × (4 − 25)
W = 10 × (−21)
W = −210 J
Answer:
The work done by the force is −210 joules
📘 Chapter Questions
- Q1. Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
- Q2. A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
- Q3. Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher.
- Q4. What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
- Q5. 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.
- Q6. A certain Household has consumed 250 units of energy during a month. How much energy is this in Joules?
- Q7. Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?
- Q8. What are the various energy transformations that occur when you are riding a bicycle?
- Q9. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
- Q10. A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational Force?Explain your answer.
- Q11. 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.
- Q12. A battery lights a bulb. Describe the energy changes involved in the process.
- Q13. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?