1. A jet airplane has an instantaneous acceleration of 2.04 m/s2 at an angle of 20.6° above the horizontal. Compute the horizontal and vertical components of force exerted on a 54.0 kg passenger by the airplane seat.
horizontal force =
verticle force =
2. You are holding a bulletin board weighing 9.39 N in place against a wall while your friend secures it to the wall. To keep it from slipping, you apply a force perpendicular to the bulletin board, pressing it directly into the wall. How large must this force be if the coefficient of static friction with the wall is 0.45?
3. A wooden block weighing 9 N is at rest on top of a wooden desk. The coefficient of static friction between the block and the desk is 0.44. Find the minimum horizontal force required to move the block if the following occurs.
(a) The block is being pressed into the surface with a 4 N force.
(b) The block is partially supported by a vertical string under a tension of 2 N.
Answers & Comments
Verified answer
2. The friction force must equal the weight:
µ * P = mg
0.45 * P = 9.39 N
P = 20.9 N
3. (a) friction Ff = µ(mg + P) = 0.44 * (9N + 4N) = 5.7 N
(b) Ff = 0.44 * (9N - 2N) = 3.1 N
In each case, the max static friction force is equal to the minimum horizontal load that must be applied in order to set the block in motion.