A raindrop of mass is 1.0 mg falls at 3 m/s when there is no wind. find its Kinetic energy when a wind of 5 m/s is blowing.
The mass of the rain drop is 1 mg or 10^-6 kg. A body that has a mass m and which is moving at a velocity v m/s has a kinetic energy equal to (1/2)*m*v^2.
The velocity of the rain drop when there is no wind blowing is 3 m/s. This gives the kinetic energy of the raindrop as (1/2)*10^-6*9 = 4.5*10^-6 J.
As only the velocity of the wind is given with no information on how that influences the the path of the rain drop it is assumed that when the wind blows at 5 m/s it contributes to increasing the velocity of the raindrop by the same magnitude. This makes the velocity of the rain drop equal to 3 + 5 = 8 m/s.
The kinetic energy of the rain drop is equal to (1/2)*10^-6*64 = 32*10^-6 J.