This post contains Physics Chapter 6 Notes Class 9 Numericals and Short Questions for the students. Name of this Chapter is “Work and Energy”. Hereunder you will find some solved Numericals and Short Questions with Answers.
Work and Energy: Physics Chapter 6 Notes Class 9 Numericals and Short Questions
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Q.1: Why fossil fuels are called the non-renewable form of energy?
Ans. The fossils fuels are one used to get energy and consumed completely. So there are not renewable.
Q.2: A stone of mass 500g strikes the ground with a velocity of 20 mS-¹. How much is the kinetic energy of the stone at the time it strikes the ground?
m = 500 g = 0.5 kg
v = 20 ms-¹
Since K.E = 1/2 mv²
K.E = 1/2 x 0.5 kg x (20 ms-¹)²
= 1/2 x 0.5 kg x 400 m² s-²
= 100 J
Q.3: Explain mass-energy equation.
Ans. Equation: E = m c²
Here E is energy, m is mass of the object while c is the speed of light (3 x 10⁸ m/s)
Q.4: Write the names of any four forms of energy.
(i) Mechanical Energy
(ii) Heat Energy
(iii) Electrical Energy
(iv) Sound Energy
Q.5: Define potential energy and write its equation also.
Ans. The energy possessed by a body due to its position is known as its potential energy.
Equation: P.E = mg h
Q.6: What is the unit of work, define it?
Ans. SI unit of work is joule (J).
Q.7: Define kinetic energy also write its equation.
Ans. The energy possessed by a body due to its motion is called its kinetic energy.
Equation: K.E = 1/2 mv²
Q.8: Define Efficiency.
Ans. The efficiency of a system is the ratio of the required form of energy obtained from a system as output to the total energy given to it as input.
Q.9: What is the SI unit of Power? Define it.
Ans. SI unit of power is watt (W). The power of a body is one watt if it does work at the rate of 1 joule per second ( 1 Js-¹).
Q.10: Write down the equation of Einstein and the value of C.
Ans. Einstein predicted the inter-conversion of matter and energy E = mc². The value of c is the speed of light (3 x 10⁸ ms-¹⁰)
Q.11: Differentiate between sound energy and mechanical energy.
Sound Energy: When you knock at the door, you produce sound. A sound is a form of energy. It is produced when a body vibrates.
Mechanical Energy: The energy possessed by a body both due to its motion or position is called mechanical energy.
Q.12: Define work and write its unit.
Ans. Work is done when a force acting on a body displaces it in the direction of a force.
Unit: The unit of work is Joul (J)
Q.13: Who predicted the mass-energy equation? Also, write its equation.
Ans. The relation between mass m and energy E is given by Einstein’s mass-energy equation.
Equation: E = m c²
Q.14: Define the power and write its unit.
Ans. Power is defined as the rate of doing work.
Unit: Unit of power is watt (W).
Q.15: When does a force work?
Ans. When the force acting on a body displaces it. Then work is said to be done.
Q.16: Differentiate between electrical energy and light energy.
Electrical Energy: Electricity is one of the widely used forms of energy. We use electrical energy from batteries etc.
Light Energy: Light is an important form of energy. Most of the light comes from the sun.
Q.17: The kinetic energy of a body of mass 2 kg is 25 J. Find its speed.
K.E = 25 J
m = 2 Kg
Formula K.E = 1/2 mV²
25 J = 1/2 (2 Kg) V²
25 = V²
V = 5 mS-¹
Q.18: Write two uses of wind energy.
(i) Wind power is used to turn wind turbines.
(ii) In the United States, some wind farms generate more than 1300 MW of electricity a day.
Q.19: What will be the torque If a force of 150 N is applied on a spanner of 10cm?
τ = F x L
τ = 100 x 0.1
τ = 10 Nm