a. Rain drop falling with constant speed:

When a rain drop falls at constant speed, its acceleration is zero (a = 0).

According to Newton's Second Law: F = ma = 0

The gravitational force (weight) is exactly balanced by air resistance, resulting in zero net force.

b. Cork floating on water:

The cork's weight is balanced by the buoyant force (upthrust) from the water.

Since the cork isn't accelerating, the net force must be zero.

Buoyant force = Weight of displaced water = Weight of cork

c. Kite held stationary in the sky:

The kite is held in place by the tension in the string balancing several forces:

- Lift from wind (upward)

- Gravity (downward)

- Air resistance (sideways)

With no acceleration, the vector sum of all forces is zero.

d. Car moving at constant velocity:

While the engine applies force to overcome friction, the net force is zero because:

- Driving force = Frictional force (in opposite direction)

With constant velocity (a = 0), F = ma = 0

e. Electron in space far from all fields:

With no gravitational, electric, or magnetic fields present:

- No forces act on the electron

- Net force is exactly zero

The electron continues moving at constant velocity (Newton's First Law).