Energy : The Driving Force – Maharashtra Board Class 9 Solutions for Science and Technology (English Medium)
- The energy stored in the dry cell is in the form of chemical energy.
- The work done is zero if there is no displacement.
- Flowing water has kinetic energy.
- By stretching the rubber strings of a catapult we store potential energy in it.
Work is the product of the force acting on the body and the displacement of the body.
W = Fs
Energy is the capacity to do work.
Power is rate of doing work.
The energy possessed by a body by virtue of its motion is called kinetic energy.
The energy possessed by a body because of its shape or position or configuration is called potential energy.
PE = mgh
- Dams are constructed on the river to store a large quantity of water at a great height so that it has potential energy.
- This potential energy can be converted into kinetic energy by allowing water to flow under gravity to a lower level.
- The kinetic energy can be converted into electrical energy using turbines and generators. Therefore, dams are constructed on the river.
- In a river, water is flowing which exerts a force on the swimmer. The swimmer has to overcome this resistive force and hence requires a lot of energy.
- While in a swimming pool, there is no flow of water, so the swimmer does not have to overcome the resistive force. Therefore, it is easy to swim in a swimming pool than in a river.
In this case, the displacement of a body is in the direction of force (F) applied on the body as shown in the figure
So, the work done by the force is given by
W = Fs
Let ‘m’ be the mass of a moving body.
Let ‘u’ be the initial velocity, ‘v’ be the final velocity and ‘a’ be the acceleration of the body.
Using the equation of motion, we get
|KE (J)||m(kg)||v (m/s)|
Data: M = 17 kg, g = 9.8m/s2, s = 2 m, W = ?
Force applied = mg
= 17 kg × (9.8 m/s2)
= 166.6 N (downward)
Force applied by Ajit to lift the load
= 166.6 N (upward)
W = Fs
= 166.6 × 2 m = 333.2 J
The work done by Ajit is 333.2 J.