An object of mass 2 kg is taken to a height 5 m from the ground `(g = 10ms^(-2))`.
(a) Calculate the potential energy stored in the object
(b) Where does this potential energy come from?
(c) What external force must act to bring the mass to that height?
(d) What is the net force that acts on the object while the object is taken to the height `h`?

Explanation

(a) `"The potential energy U"=mgh =2xx10xx5=100J` Here the positive sign implies that the energy is stored on the mass.
(b) This potential energy is transferred from external agency which applies the force on the mass
(c) The external applied force `vecF_(a)`, which takes the object to the height 5 m is, `vecF_(a)=-vecF_(g)`
`vecF_(a)=-(-mghatj)mghatj`
where, `hatJ` represents unit vector along vertical upward direction
(d) From the definition of potential energy, the object must be moved at constante So the net force acting on the object is zero
`vecF_(g)+vecF_(a)=0`