$A$ boy pushes the wall in the class for five minutes but the wall does not move. Another boy pushes the chair from the front to the back side of the class. In which case,more work is done?

Define watt. Express kilowatt in terms of joule per second. $A$ $150 \, kg$ car engine develops $500 \, W$ for each $kg$. What force does it exert in moving the car at a speed of $20 \, m \, s^{-1}$ (in $N$)?

$(a)$ Define one watt.
$(b)$ $A$ lamp consumes $1000 \ J$ of electrical energy in $10 \ s$. What is its power?

When a force retards the motion of a body,the work done is:

What is the work done by the tension in the string of a simple pendulum?

$(i)$ An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the total work done against the force of gravity and by the force of gravity on the object? Explain with proper mathematical expression.
$(ii)$ $A$ certain force acting on a $20 \, kg$ mass changes its velocity from $5 \, m s^{-1}$ to $2 \, m s^{-1}$. Calculate the work done by the force.