33. Give reasons for the following:
(a) No work is done if a man is pushing against
a wall.
(b) Hammer drives a nail into the wood only
when it is lifted up and then struck.
(c) A horse and a dog are running with the same
speed. Which one of them has more kinetic
energy than the other ?
(d) A teacher moving around in the class is doing
work but a child standing and reading a book
is not doing any work.
Answers
Answer:
(a) Even though the man exerts force on the wall , the wall does not move. Work done = force applied * displacement and since the displacement of the wall is zero. , work done is also zero.
(b) It is true that the hammer drives the nail into the wood only when it is lifted and then struck. The sum of the potential and kinetic energy that the hammer acquired to drive in the nail is called the Mechanical energy, which results in the work done.
(c) If a dog and horse are running with the same speed, kinetic energy of horse is more than the kinetic energy of the dog because the mass of a horse is more than the dog. So, more the mas more the kinetic energy is.
(d) Because Teacher is in motion and it has kinetic energy.But according to the definition of work -work is said to be done if the force applied on a body moves it if no motion take place no work is said to be done. So a child reading a book is not doing work
Explanation:
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