I am badly stuck on a few Newton's Laws problems. I hope someone can help me out! Thanks a million! Please Register or Log in to view the hidden image! 1) A 5 kg block rests on a 30 degrees incline. The coefficient of static friction between the block and incline is 0.20. How large a horizontal force must push on the block if the block is to be on the verge of sliding 1a) up the incline? 1b) down the incline? I really have no clue of solving this. Would 1a and 1b have the same answer? 2) A double incline plane has two boxes of equal masses on opposite sides connected by a rope over a pulley. The left incline is 53 degrees and the right incline is 30 degrees. The coefficient of static and dynamic friction are equal, 0.30 for both boxes. 2a) Show that the system, when released, remains at rest. 2b) If the system is given an initial speed of 0.90m/s to the left, how far will it move before coming to rest? For 2a, I know that the motion of attempted of the system is to the left beucase the left incline is steeper and the boxes have equal masses. So there are 2 frictional forces, both pointing to the right. Knowing all these, I got that the acceleration is 0.69441m/s^2 . Then, how can the system remain at rest? Can someone explain? I don't understand. For 2b, v1=-0.90m/s, v2=0, a=0.69441. Using these, I found that the system moves 0.58m to the left before coming to rest. But can I use the acceleration that I got in part a? Is this the correct way of doing it? 3) The radius of the earth is about 6370km, while that of Mars is 3440km. If an object weights 200N on earth, what would it weight, and what would be the acceleration due to gravity, on Mars? Mars has a mass 0.11 that of earth. I tried using law of universal gravitation equation and it works. I am wondering if there is any way of solving this problem without the use of the law of universal gravitation beucase this equation is not taught in my course yet.