Question

A raindrops of mass 1 g falling from a height of 1 km hits the ground with a speed of 50 m/s . of the resistive force is proportional to the speed of the drop then the work by the resistive force is??? ( g=10)​

Answer 1

Solution :-

• mass of the drop(m) = 1g = 0.001 kg

• Height from the ground(h) = 1 km = 1000 m

• speed with which the raindrop hits the ground(v) = 50 m/s

As per the formula ,

➽ W = Δ KE

➽ Wr + Wg = ΔKE

here ,

• Wr = work done due to resistive force
• Wg = work done by gravitational force
• KEi = initial kinetic energy
• KEf = final kinetic energy

Here ,

➺ ΔKE = KEf -KEi

➺ ΔKE = mv²/2- mu²/2

➺ ΔKE = mv² /2                 (∵ u=0 )

➺ ΔKE = 0.001 x 2500 /2

➺ ΔKE = 1.25 J

Work done by gravitational force is given by ,

➸ Wg = mgh

➸ Wg = 0.001 x 10 x 1000

➸ Wg = 10 J

Now let's substitute these values in the above equation ,

➝ Wr + 10 = 1.25

➝ Wr = 1.25 - 10

➝ Wr = - 8.75 J

The resistive force acting on the raindrop is 8.75 J