This set of Physics Question Paper focuses on “Various Forms of Energy : The Law of Conservation of Energy”.
1. Which of the following statements are true?
a) Energy can be created and destroyed
b) Energy cannot be created but only destroyed
c) Energy cannot be destroyed but only created
d) Energy can neither be created nor destroyed
Explanation: According to the law of conservation of energy, energy can neither be created nor destroyed but can only be changed from one form to another. This is also one of the fundamental concepts of thermodynamics.
2. The dimensions of energy are _____
Explanation: Energy = Force x Displacement
Units of energy = kg x (m/s2) x m
= kg x m2 x s-2
Dimensions of energy = [ML2T-2].
3. Which of the following is not true?
a) Energy of an open system can be varied
b) Energy cannot be created
c) Energy cannot be destroyed
d) Energy cannot be transformed
Explanation: According to the law of conservation of energy, energy can neither be created nor destroyed but can only be changed from one form to another. Energy in an open system can be varying because of constant matter and radiation exchanges with the surrounding universe.
4. The law of conservation of energy is not applicable to mechanical systems as they require energy input to keep working.
Explanation: The law of conservation of energy is applicable to mechanical systems but it may not necessarily be applicable to a “machine” that requires constant power input to operate because it would then essentially be an open system.
5. The energy possessed by an object because of its motion is termed _____
a) potential energy
b) kinetic energy
c) nuclear energy
d) solar energy
Explanation: An object in motion possesses a velocity “v” at any instant of time.
This energy is termed “kinetic energy” and is given by;
Kinetic Energy = 1/2 x m x v2
m = Mass of the object in motion
6. The maximum potential energy in a roller coaster is at _____
a) the top of the steep climb
b) somewhere during the climb
c) somewhere during the descent
d) the lowest point after the climb
Explanation: The potential energy is given by;
PE = m x g x h
PE = Potential energy
m = Mass of the object
g = Acceleration due to gravity
h = Height of the object
Hence, the higher the object, the greater the potential energy.
7. Fire is a form of _____
a) solar energy
b) thermal energy
c) gravitational energy
d) kinetic energy
Explanation: Thermal energy is the consequence of the temperature of an object that is transferred in the form of heat from a source of greater temperature to a region or object of lower temperature by modes such as conduction, convection or radiation.
8. When a roller coaster is at the top of a steep hill, its potential energy is maximum. When it hurdles down the slope and comes to the bottom, the potential energy reduces greatly. Hence we can say that the law of conservation of energy is not valid here since energy is destroyed.
Explanation: When a roller coaster is at the top of a steep hill, its potential energy is maximum. When it hurdles down the slope and comes to the bottom, the potential energy reduces greatly. However, kinetic energy increases. Thus, there is a change from potential energy to kinetic energy and hence no destruction of energy.
9. When a person intakes 3000 kcal of food, he is able to do work requiring energy of 2500 kcal. This means that the human body destroys a fraction of energy obtained from food.
Explanation: If a person consumes 3000 kcal of food and does a work requiring 2500 kcal of energy, the rest of the 500 kcal is mostly used for the metabolic activities of the body and some are lost in the form of heat energy to the atmosphere.
10. For a freely falling body, which of the following quantities will not change?
a) Total kinetic energy
b) Total potential energy
c) Total mechanical energy
d) Insufficient data
Explanation: For a body falling freely under the influence of gravity, the velocity increases as heigh decreases. Hence, there is a reduction in potential energy but an increase in kinetic energy. However, the total mechanical energy, i.e., the sum of potential and kinetic energy always remains constant as per the law of conservation of energy.
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