true or false

Question 11 Mark

The potential energy of a body of mass 1kg kept at a height of 1m is 1J?

Answer

False.
PE = m × g × h
= 1 × 9.8 × 1
= 9.8J

Question 21 Mark

Work done by gravity on a man moving on horizontal surface is negative.

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 × D × 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 × D × 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.

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

Kinetic energy + Potential energy = Mechanical energy.

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 51 Mark

Energy does not remain conserved in an oscillating pendulum.

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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