Under the action of a force of 15 n, a body weighing 3 kg changed its speed by 15 m / s. How long did the force last?

Newton’s second law: F = m * a, where F is force, m is mass, a is acceleration.
The data in the task will allow you to find the acceleration. Let’s express it from the formula. a = F / m. Let’s plug in the numbers. a = 15 N / 3 kg = 5 m / s ^ 2
There is another formula for finding acceleration. a = ΔU / t,
where ΔU is the change in speed, t is time. Let’s express the time. t = ΔU / a
Let’s plug in the numbers. t = (15m / s) / (5m / s ^ 2) = 3 s.
Answer: 3 s