A box C C\,C of mass 3 kg is held at rest on a rough surface inclined at an angle α \alpha\,α to the horizontal, where cosα=0.8\cos \alpha = 0.8cosα=0.8. It is connected to a box D D\,D of mass 7 kg by a light inextensible string passing over a smooth pulley. D D\,D hangs vertically. The string is parallel to the slope. The coefficient of friction between C C\,C and the plane is 0.25. The system is released from rest.
Find the tension in the string as the boxes accelerate.
Once D D\,D reaches the floor, C C\,C continues to move up the plane until it stops. Determine whether box C C\,C will remain at rest in its highest position.
Suggest two refinements to the model that would make it more realistic.
25 exam-style questions on WJEC A Level Maths 4.9.5 Forces and Newton's laws (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.