Question

A body of mass 1kg falls from rest through a distance of 200
m and acquires a speed of 50 m/s. Work done against friction
of air is ( Take g = 10m/s2)

a) 700 J
b) 1250 J
c) 750 J
d) 2000 J​

Answer 1

Explanation:

GIVEN:-

=> Mass = 1kg

=> Height = 200m

=> Velocity = 50m/s

TO FIND:-

=>Work done against friction of air.

UNDERSTANDING THE CONCEPT:-

According to the question,

=> We know that in Work, Power, Energy,

Work done due to all forces = change in kinetic energy.

=>So, From all the provided details, Let us conclude our answer by using the respective formula.

CONCEPT REFRESHER:-

=>The formula is,

$\sf{Gravity + Air \: friction = \dfrac{1}{2}mv {}^{2} }$

ANSWER:-

=>Using this formula,

$\sf{1 \times 10 \times 200+\: friction = \dfrac{1}{2} \times 1 \times 50 {}^{2} }$

$\sf{Air \: friction = \frac{1}{2} \times 1 \times 50 {}^{2} - 1 \times 9.81 \times 200}$

$\sf{Air \: friction = - 750j}$

=> Negative sign indicates work is against the displacement. Therefore, The work done is 750J.