What is the amount of work done by a force when a body moves in a circular path?

$(i)$ 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.

An automobile engine propels a $1000 \,kg$ car $(A)$ along a levelled road at a speed of $36 \,km \,h^{-1}$. Find the power if the opposing frictional force is $100 \,N$. Now,suppose after travelling a distance of $200 \,m$,this car collides with another stationary car $(B)$ of the same mass and comes to rest. Let its engine also stop at the same time. Now car $(B)$ starts moving on the same level road without its engine started. Find the speed of the car $(B)$ just after the collision.

$A$ body is moving with constant speed over a frictionless surface. What is the work done by the weight of the body?

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

$A$ body moves along a circular path. How much work is done in doing so? Explain.