In rectilinear motion with constant acceleration, the modulus of the body’s velocity has decreased

In rectilinear motion with constant acceleration, the modulus of the body’s velocity has decreased from rx = 8.0 m / s to ∨ = 4.0 m / s. In this case, the body has passed the path s = 21 m. In what period of time did this happen?

Data: rectilinear uniformly accelerated motion; V1 (initial speed) = 8 m / s; V2 (final speed) = 4 m / s; S (distance traveled) = 21 m.

To determine the time interval during which a given body changed its speed, we apply the formula: S = (V2 + V1) * t / 2, whence t = 2S / (V2 + V1).

Let’s make a calculation: t = 2 * 21 / (4 + 8) = 42/12 = 3.5 s.

Answer: The given body reduced its speed in 3.5 s.