How many watts are there in $1$ horsepower (in $watts$)?

$(a)$ Define work. State two factors on which the magnitude of work depends.
$(b)$ $A$ car and a truck have the same speed of $30 \, m/s$. If their masses are in the ratio $1:3$,find the ratio of their kinetic energy.

In case of negative work,the angle between the force and displacement is: (in $^o$)

$A$ 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?

An iron sphere of mass $30 \, kg$ has the same diameter as an aluminium sphere whose mass is $10.5 \, kg$. The spheres are dropped simultaneously from a cliff. When they are $10 \, m$ from the ground,they have the same:

Calculate the kinetic energy of a car of mass $750\, kg$ moving with a velocity of $54\, km h^{-1}$. Find the new kinetic energy of the car if a passenger of mass $50\, kg$ sits in the car.