A body weighing 400 g is lifted vertically upward from a state of rest, applying a force of 4.2 N. What speed will this body acquire

A body weighing 400 g is lifted vertically upward from a state of rest, applying a force of 4.2 N. What speed will this body acquire in 2 seconds of movement? Wind resistance is not considered.

m = 400 g = 0.4 kg.

g = 10 m / s ^ 2.

V0 = 0 m / s.

F = 4.2 N.

t = 2 s.

V -?

Let us write Newton’s 2 law for a body when moving upward: m * a = Fр, where m is the mass of the body, a is the acceleration of the body, Fр is the resultant of all forces that act on the body.

Two forces act on the body: vertically upward force F, vertically downward force of gravity m * g.

Their resultant will have the form: Fр = F – m * g.

2 Newton’s law will take the form: m * a = F – m * g.

Let’s write the formula for determining the acceleration of the body: a = (V – V0) / t.

Since V0 = 0 m / s, then a = V / t.

m * V / t = F – m * g.

The formula for determining the speed will be: V = (F – m * g) * t / m.

V = (4.2 N – 0.4 kg * 10 m / s ^ 2) * 2 s / 0.4 kg = 1 m / s.

Answer: the body will have a speed V = 1 m / s.