The inclined plane makes an angle α = 30 ° with the horizon. The body was laid on the plane and pushed up

The inclined plane makes an angle α = 30 ° with the horizon. The body was laid on the plane and pushed up. During the time t1 = 0.7 s, the body passed the distance l = 1.4 m, after which it began to slide down. How long does it take to slide to the starting position of the body? What is the coefficient of friction of the body against an inclined plane?

Obviously, the ascent time is equal to the descent time.
Let’s find the acceleration with which the body moved:
l = a * t ^ 2/2
a = t ^ 2 / 2l = 0.7 ^ 2 / 1.4 * 2 = 0.7 / 4 = 0.175 m / s ^ 2
Let’s write the projection of Newton’s second law onto the axis coinciding with the motion of the body:
Ftr = ma
k * mg * sinα = ma
k = a / g * sinα = 0.175 / 10 * 1/2 = 0.035.