Question

5 -kg crate is on a plane inclined 30 degree above the horizontal . A force of 20 nt is used to move it upwards . After how many seconds will the crate attain a velocity of 2.78 m/sec if the coefficient of friction between the crate and the plane is 0.30?

Answer 1

$$v=at=\frac{(F-mg(\sin{30}+\mu \cos{30}))}{m}t\\ 2.78=\frac{(20-5(9.8)(\sin{30}+0.3 \cos{30}))}{5}t\\t=-0.8\ s<0\ s$$

Thus, the body cannot move upwards:

$$F<mg(\sin{30}+\mu \cos{30})$$