Question

Give the magnitude and direction of the net force acting on
a) a drop of rain falling down with a constant speed,
b) a cork of mass 10 g floating on water,
c) a kite skilfully held stationary in the sky,
d) a car moving with a constant velocity of 30 km/h on a rough road,
e) a high-speed electron in space far from all material objects, and free of electric and magnetic fields.

Answer 1

a) Zero net force
The rain drop is falling with a constant speed.
Hence, it acceleration is zero. As per Newton’s second law of motion, the net force acting on the rain drop is zero.

b) Zero net force
The weight of the cork is acting downward. It is balanced by the buoyant force exerted by the water in the upward direction.
Hence, no net force is acting on the floating cork.

c) Zero net force
The kite is stationary in the sky, i.e., it is not moving at all.
Hence, as per Newton’s first law of motion, no net force is acting on the kite.

d) Zero net force
The car is moving on a rough road with a constant velocity.
Hence, its acceleration is zero. As per Newton’s second law of motion, no net force is acting on the car.

e) Zero net force
The high speed electron is free from the influence of all fields.
Hence, no net force is acting on the electron.