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Work, Power And Energy · MP Board (MPBSE) STD 9 (Madhya Pradesh - English Medium). 5 questions.

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Question 11 Mark
Kinetic energy + Potential energy = Mechanical energy. [True/ False]
Answer
True. Explanation: Mechanical energy is the sum of kinetic and potential energy in an object that is used to do work. In other words, it is energy in an object due to its motion or position, or both.
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Question 21 Mark
Work done by gravity on a man moving on horizontal surface is negative. [True/ False]
Answer
False.
Explanation: The force exerted by gravity is downward so the block should move downward. but, here the block is moving horizontally so work is not done by gravity. Mathematically, $W = F \times D \times $ cos Where is the angle between force and displacement. Here is 90 degree as direction of force and displacements of block are perpendicular to each other. So, $W = F \times D \times Cos\ 90 = 0J$
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Question 31 Mark
No, matter what is the magnitude of mass falling from a height, its acceleration is always the same. [True/ False]
Answer
True.
Explanation: Objects with greater mass feel a greater the force on them. However, the acceleration due to gravity, g, is the same for all objects, no matter what their mass. This means that all objects will accelerate or fall at the same rate, provided they are not affected by air resistance.
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Question 41 Mark
Energy does not remain conserved in an oscillating pendulum. [True/ False]
Answer
False.
Explanation: Simple pendulum, mechanical energy is conserved. The kinetic energy would be $\text{KE}=\frac{1}{2}\text{mv}^2$ where m is the mass of the pendulum, and v is the speed of the pendulum. However, the total energy is constant as a function of time.
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Question 51 Mark
State whether the following statement is true or false:
The potential energy of a body of mass $1kg$ kept at a height of $1m$ is $1J$?
Answer
False. $PE = m \times g \times h = 1 \times 9.8 \times 1 = 9.8J$
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