Question

2. Find out the expression for –
(a) Potential energy (b) Kinetic energy

Answer 1

Explanation:

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Answer 2

Answer:

Explanation:

Potential Energy derivation:

Let a body of mass m be raised up through height h from the ground. the body will acquire potential energy equal to the work done in lifting it to height h.

Thus Potential energy = F× h

                                     =w×h

(Here weight of the body = w =mg)

     ∴                  P.E = w h = mgh

Derivation of kinetic energy:

consider a body of mass m moving with velocity v. the body stops after moving through some distance S due to some opposing force such as force of friction acting on it. the body posseses kinetic energy and is capable to do work against opposing force F until all of its Kinetic energy is used up.

∴K.E of the body = work done by it due to motion

                        K.E   = F S

                         vi   =  v

                         vf   = 0

As                    F =  ma

    ∴            a=  - $\frac{F}{m\\}$

  Since motion is opposed, hence, a is negative.

using 3rd equation of motion:

                 2 a S =  vf ² - vi²

               2(- $\frac{F}{m\\}$ ) S = (0)² - (v)²

              F S =   $\frac{1}{2}$  m v²

      ∴    K.E =  $\frac{1}{2}$  m v²