(a) Explain by an example what is meant by potential energy. Write down the expression for gravitational potential energy of a body of mass m placed at a height h above the surface of the earth.
(b) What is the difference between potential energy and kinetic energy?
(c) A ball of mass 0.5 kg slows down from a speed of 5 m/s to that of 3 m/s. Calculate the change in kinetic energy of the ball. State your answer giving proper units.
(a) Explain by an example what is meant by potential energy. Write down the expression for gravitational potential energy of a body of mass m placed at a height h above the surface of the earth.
(b) What is the difference between potential energy and kinetic energy?
(c) A ball of mass 0.5 kg slows down from a speed of 5 m/s to that of 3 m/s. Calculate the change in kinetic energy of the ball. State your answer giving proper units.
(a) This is energy that is stored due to an object's position. It is dependent on the mass of the object, the height of the object above the ground or Earth, and the acceleration due to gravity.
Examples of Potential Energy:
1. A rock sitting at the edge of a cliff has potential energy. If the rock falls, the potential energy will be converted to kinetic energy.
2. Tree branches high up in a tree have potential energy because they can fall to the ground.
Expression for Potential Energy:
Consider a body of mass m lying at point A on the earth's surface, where its potential energy is taken as zero.
Weight of object = mg, acting vertically downwards.
In order to lift the body to another position B at a height h, we have to apply a minimum force equal to mg in the upward direction.
So work is done on the body against the force of gravity, is given by Work done = Force × Displacement, W = Fs
But,
F = mg and s = h,
Therefore, W = mg × h = mgh
The work done (mgh) on the body is equal to the gain in energy of the body. This is the potential energy (EP) of the body.
Thus, Ep = mgh
(b) Kinetic Energy:
1. The energy possessed by an object by the virtue of its motion.
2. It is measured from the place itself.
3. It is measured by mass and velocity.
4. Example: Falling coconut, moving car or bus etc.
Potential Energy:
1. The energy possessed by an object by the virtue of its shape, position and configuration.
2. It is measured by mass, gravitational force and height.
3. This is the energy which is stored at a height.
4. Example: Stretched rubber band, slinky, an arrow and a stretched string of the bow etc.
(c) K.E.1 = 12 mv2 = 12 × 0.5×5×5 = 6.25 J
K.E.2 = 12 mv2 = 12 × 0.5×3×3 = 2.25 J
Change in kinetic energy = 6.25 - 2.25 = 4 J
(a) This is energy that is stored due to an object's position. It is dependent on the mass of the object, the height of the object above the ground or Earth, and the acceleration due to gravity.
Examples of Potential Energy:
1. A rock sitting at the edge of a cliff has potential energy. If the rock falls, the potential energy will be converted to kinetic energy.
2. Tree branches high up in a tree have potential energy because they can fall to the ground.
Expression for Potential Energy:
Consider a body of mass m lying at point A on the earth's surface, where its potential energy is taken as zero.
Weight of object = mg, acting vertically downwards.
In order to lift the body to another position B at a height h, we have to apply a minimum force equal to mg in the upward direction.
So work is done on the body against the force of gravity, is given by Work done = Force × Displacement, W = Fs
But,
F = mg and s = h,
Therefore, W = mg × h = mgh
The work done (mgh) on the body is equal to the gain in energy of the body. This is the potential energy (EP) of the body.
Thus, Ep = mgh
(b) Kinetic Energy:
1. The energy possessed by an object by the virtue of its motion.
2. It is measured from the place itself.
3. It is measured by mass and velocity.
4. Example: Falling coconut, moving car or bus etc.
Potential Energy:
1. The energy possessed by an object by the virtue of its shape, position and configuration.
2. It is measured by mass, gravitational force and height.
3. This is the energy which is stored at a height.
4. Example: Stretched rubber band, slinky, an arrow and a stretched string of the bow etc.
(c) K.E.1 = 12 mv2 = 12 × 0.5×5×5 = 6.25 J
K.E.2 = 12 mv2 = 12 × 0.5×3×3 = 2.25 J
Change in kinetic energy = 6.25 - 2.25 = 4 J
