question_answer 1)

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, [Delhi 12] (e) a high-speed electron in space far from all gravitating objects, and free of electric and magnetic fields.  

Answer:

(a) As the rain drop is falling down with a constant speed, no net force is acting on it. The weight of the drop is balanced by the upthrust and viscosity of air. (b) Zero, because the weight of the cork is balanced by the upthrust exerted by water. (c) As the kite is held stationary, no net force acts on it. The force exerted by air on the kite is balanced by the tension produced in the string. (d) As the car is moving with a constant velocity, no net force acts it. The force exerted by the engine is balanced by the friction due to rough road. (e) As no field (gravitational/electric/magnetic) is acting on the electron, the net force on it is zero.