KnowledgeBoat Logo

Physics

(a) A runner of mass 60 kg runs upstairs and reaches the 10 m high first floor in 4 s.

Calculate the

I. force of gravity acting on him

II. work done by him against gravity and

III. power developed by the runner.

(b) Give two examples in which mechanical energy is conserved.

Work, Energy & Power

8 Likes

Answer

(a) Given,

Mass of runner = 60 kg

Gravitational force = g = 10ms-2

I. Force of gravity acting on runner = mg = 60 x 10 = 600 N

Hence, force of gravity acting on him = 600 N

II. Work done by runner against gravity = mgh = 60 x 10 x 10 = 6000 J or 6 kJ

Hence, Work done by runner against gravity = 6 kJ

III. Power developed by the runner,

P = wt\dfrac{\text{w}}{\text{t}}

= 60004\dfrac{6000}{4}

= 1500 W

Hence, power developed by the runner = 1500 W

(b) Two examples in which mechanical energy is conserved are:

  1. Motion of a simple pendulum.
  2. Free fall of a body under gravity.

Answered By

5 Likes

Related Questions