A truck is hauling a 300-kg log out of a ditch using a winch attached to the back of the truck. Knowing the winch applies a constant force of 2650 N and the coefficient of kinetic friction between the ground and the log is 0.45, determine the time for the log to reach a speed of 0.5 m/s.

  t = 0.113 s

Explanation:

In this exercise we can use Newton's second law

X Axis            F - fr = ma

Y Axis           N –W = 0

                    N = W = m g

The force of friction is

                  fr = μ N

We replace

                 F - μ m g = m a

                  a = (F- μ mg) / m

                 a = (2650 - 0.45 300 9.8) / 300

                 a = 4,423 m / s2

Now we can use the kinematics expressions, where we assume that the system starts with zero speed

                v = v₀ + a t

                t = v / a

                t = 0.5 / 4.423

                t = 0.113 s