An object of mass 2 kg falls from a height of 5 m to the ground. What is the work done by the gravitational force on the object? (Neglect air resistance, Take g = 10 m `s^(-2)`)

Explanation

In this case the force acting on the object is downward gravitational force `mvec(g)`. This is a constant force.
Work done by gravitational force is
`" "W=int_(r_(i))^(r_(f))vec(F)*dvec(r)`
`W=(Fcostheta)int_(r_(i))^(r_(f))dr=(mgcostheta)(r_(f)-r_(i))`.
The object also moves donwward which is in the direction of gravitational force `(vec(F)=mvec(g))` as shown in figure. Hence, the angle between them is `theta=0^(@), cos0^(@)=1` and the displacement, `(r_(f)-r_(i))=5m`
`" "W=mg(r_(g)-r_(i))`
`" "W=2 times emptyset times 5 = emptyset`
The work done by the gravitational force on the object is objective.