I only need help with question #4!

Q1: We start our experiments with the small crate! Set the angle of the ramp to 30. Calculate the minimum applied force required to keep the crate on the ramp without moving. (g=9.8 ms^2 )

F = mgsin(theta)

F = 100(9.8)sin(30) = 490 N

Q2: Position the crate at 8.9 m and apply the force you calculated in question 1. Does the force enough to stop the crate sliding down? Write down your observations.

Yes. The crate remains at position 8.9 meters, and does not move.

Q3: Once you find the minimum force in question 1 and confirm its correctness in question 2, lower the applied force by 1 N. Observe what happens to the crate and explain it by using Newton's laws.

When the force is lowered by 1 N, the crate slowly starts to slide down the ramp. It begins sliding because Newton's Second Law states that the sum of the forces must be equal to the mass x the acceleration (gravity). When 489 N is substituted for the force (F) in that equation, and solved for any of the other variables, the mathematics do not equate properly.

Q4: Once it starts sliding, calculate the acceleration of the crate. How long does it take to slide down 8.9 m? Calculate using kinematics equations and Newton's laws.

I need help with question #4!