Question

Question 5.1 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 skillfully 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.

Chapter Laws Of Motion Page 109

Answer 1

a) net force is 0(as the drop is falling with constant acceleration)
b) net force is 0(the weight of the cork is balanced by the upward buoyant force)
c) net force is 0(by Newton's 2nd law of motion)
d) net force is 0(the force of friction by the accelerator is balanced by the force of friction between the tyres and the rough road)
e) net force is 0(as no field, electric, magnetic or gravitational, is acting on the electron)

Answer 2

(a) net Force = 0 , because a drop of rain falling with constant speed .e.g acceleration = 0
But we know ,
F = ma
= m× 0 = 0

(B) we know according to Archimedes's concept ,
Body floating it means upward force is balanced by downard force ( weight ).
e.g Fnet = 0
Hence, net Force acting on a cork of mass 10g = 0.

(C) a kite skillfully held stationary in the sky , it means sky is in rest hence acceleration of kite = 0 . e.g F = ma = 0

(D) car is moving with constant velocity so, acceleration = 0
Hence, net Force acting on car = 0.

(E) Electron isn't experiencing , electric, magnetic and gravitational field .hence, net Force acting on electron in free space = 0