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 \[10g\] floating on water
C. A kite skillfully held stationery
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

Hint: The net force acting on a particle is equal to the algebraic sum of all forces acting on it from all directions.

Complete step by step solution:
A. As the raindrop is falling with a constant speed, so its acceleration a will be 0. As the force acting on a particle is given by , so the net force acting on the rain drop will be 0.

B. When a cork floats on water, two forces will act on it. One of them is the weight of the cork acting vertically downwards and the other is the upthrust by water acting vertically upwards. As the cork is floating on water, so the two forces acting on it balance each other. Hence the net force acting on the cork will be 0.

C. As the kite is held stationary, so by Newton's first law of motion, the algebraic sum of forces acting on the kite is zero.

D. When a car moves on a rough road, three forces will act on it, its weight acting vertically downwards, the normal reaction by the road acting on it vertically upwards. These two forces balance each other. The third force will be the frictional force acting opposite to the motion of the car. As the car is moving with a constant velocity, so its acceleration will be zero. Hence the net force acting on the car will be 0.

E. Since, the high-speed electron is free from all material objects and no electric field and magnetic field acts on it. So, the net force acting on it will be 0.

Note: If the acceleration of a body is zero, the net force acting on it will be zero.