1)... Define the following terms and give their SI units. (a) Work (b) Power (c) Energy
(ans) --Work is done when a force acts on an object, causing it to move in the direction of the force. The amount of work done is equal to the product of the force and the distance the object moves. joule (J)
--Power is the rate at which work is done. It is measured in joules per second. watt (W)
--Energy is the ability to do work. It exists in many different forms, including potential energy, kinetic energy, thermal energy, and chemical energy. joule (J)
2)... List different forms of energy.
(ans)
Kinetic Energy: Energy of motion
Potential Energy: Stored energy due to position or configuration
Mechanical Energy: Combination of kinetic and potential energy associated with objects
Thermal Energy: Energy associated with the temperature of an object (heat)
Radiant Energy: Energy carried by electromagnetic waves (light, radio waves, etc.)
Sound Energy: Energy carried by mechanical waves (sound)
Electrical Energy: Energy associated with the flow of electric charges
Chemical Energy: Energy stored in the bonds between atoms and molecules
Nuclear Energy: Energy stored in the nucleus of atoms
Gravitational Energy: Energy associated with the position of objects in a gravitational field
Elastic Energy: Energy stored in objects due to deformation (stretched rubber band)
Magnetic Energy: Energy associated with magnetic fields
Plasma Energy: Energy associated with ionized gas
Quantum Energy: Energy associated with the behavior of matter at the atomic and subatomic level
3)... State Law of Conservation of Energy. Explain with the help of examples.
(ans)
Rolling Ball: Imagine a ball rolling down a hill. As it descends, its potential energy (due to its height) decreases, while its kinetic energy (due to its speed) increases. The total energy, however, remains the same throughout the movement. It just changes form.
Burning Wood: When wood burns, the chemical energy stored in the wood's bonds is released as heat (thermal energy) and light (radiant energy). Again, the total energy doesn't vanish, it just transforms into different forms.
Power Plant: In a power plant, various energy transformations occur. Fossil fuels release chemical energy that heats water, converting it into steam (thermal energy). The steam spins turbines, generating kinetic energy, which eventually converts into electrical energy. Throughout these transformations, the total energy stays constant.
Photosynthesis: Plants capture sunlight (radiant energy) and use it to convert carbon dioxide and water into carbohydrates (chemical energy). While the forms of energy change, the total amount remains the same.
Pendulum: A swinging pendulum showcases the constant exchange between kinetic and potential energy. As the pendulum swings up, its kinetic energy decreases while its potential energy increases. At the peak, its kinetic energy is zero, and its potential energy is maximum. On the way down, the opposite happens. The total energy, however, remains constant throughout the swing.
4)... List the energy transformation taking place in a thermal power plant.
(ans)
Chemical to Thermal Energy: The process starts with the combustion of fossil fuels like coal, natural gas, or oil. This combustion reaction releases chemical energy stored in the bonds of the fuel molecules and converts it into thermal energy in the form of heat.
Thermal to Mechanical Energy: The heat generated in the furnace is used to heat water in a boiler. As the water temperature rises, it turns into steam. This high-pressure, high-temperature steam expands rapidly and pushes against the blades of a turbine, converting thermal energy into mechanical energy of rotation.
Mechanical to Electrical Energy: The rotating turbine shaft is connected to a generator, which is essentially a large electromagnet. The spinning motion of the shaft induces an electric current in the generator's conductors, transforming mechanical energy into electrical energy.
Thermal to Kinetic Energy: A small portion of the thermal energy is lost to the environment through cooling towers or heat exchangers. This lost heat can sometimes be used for district heating applications.
Electrical to Magnetic Energy: The electrical energy generated by the plant creates magnetic fields when transmitted through power lines.
Electrical to Various Forms: Once the electricity reaches homes and businesses, it is transformed into various other forms depending on its use, such as light energy, heat energy, kinetic energy (motors), and sound energy.
5)... A ball of mass 0.5 kg has 100 J of kinetic energy. What is the velocity of the ball?
(ans)
The formula for kinetic energy is:
KE = 1/2 m v^2
where:
KE is the kinetic energy (in joules)
m is the mass of the object (in kilograms)
v is the velocity of the object (in meters per second)
We can rearrange the formula to solve for the velocity:
v = sqrt(2 * KE / m)
Plugging in the values we know:
KE = 100 J
m = 0.5 kg
v = sqrt(2 * 100 J / 0.5 kg)
v = sqrt(400 J / kg)
v ≈ 20 m/s
Therefore, the velocity of the ball is approximately 20 meters per second.
6)... A body of mass 100 kg is lifted by 10 m. Find
(a) The amount of work done. (b) Potential energy of the body at that height (g =10 ms–2)
(a) Force = 100 kg × 10 m/s² = 1000 N
Now, calculate the work done:
Work done = 1000 N × 10 m = 10000 J
Therefore, the amount of work done to lift the 100 kg object 10 meters is 10,000 Joules.
(b)mass = 100 kg
g = 10 m/s²
height = 10 m
Potential energy = 100 kg × 10 m/s² × 10 m = 10000 J
Therefore, the potential energy of the 100 kg object at a height of 10 meters is also 10,000 Joules.