On an inclined plane with an angle of inclination of 30 degrees, the bar descended after passing a path of 7m.

On an inclined plane with an angle of inclination of 30 degrees, the bar descended after passing a path of 7m. How long does the descent take if the coefficient of friction is 0.1

Let us write down the sum of all forces in terms of 2 s-n Newtons (putting vectors over vector forces are g, N, Ftr)
ma = mg + N + Ftr
Project on the x and y axes:
x: ma = mgsinα – Ftr
y: 0 = N – mg
Since Ftr = mg we solve this system:
ma = mgsinα – umgcosα = g (sinα – ucosα)
Let’s substitute:
g (sinα – ucosα) = 10 * (1/2 – √3 / 2 * 0.1) = 5 – √3 / 2 = 4.13 (m / s ^ 2)
There is a path and time, we find the time from the formula:
S = (a * t ^ 2) / 2
t = 1.84 (s)
Answer: t = 1.84 (c)