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# Mechanics 1 (OCR MEI A level) watch

1. Help pls, thank you
2. To help you understand these questions, I suggest redrawing the diagram with arrows labelling all of the forces and their magnitudes and directions, and which direction the acceleration is in. I have done one for you to help get you started

For 3i), you can now make equations for each block by resolving the forces.
For the block weighing 8kg, which we'll call Block A, the motion is horizontal therefore we have to resolve the horizontal forces to get this equation:
T - F = 8a. Remember that F = ma (the resultant force is the mass multiplied by the acceleration), and the block is moving in the same direction as the tension.
But since the table is said to be smooth, there is no friction, so F = 0, and the tension would therefore be 8a.

We can also resolve vertically for the block that weighs 4kg, Block B:
4g - T = 4a. Since the direction motion is downwards, the tension would be negative in this case. g = 9.8.
Now that you have your equations, you can sub in the value of T you found earlier into the equation for Block B to find the acceleration for 3ii.

For 3iii, draw another diagram showing the direction of the forces, and resolve in directions perpendicular and parallel to the plane for each of the two boxes.

Now, when the system is in equilibrium, there is no movement, therefore the equations you form when you resolve should be equal to 0, allowing you to find unknown values.
I'll get you started on one equation as an example:
For block weighing 8kg, R(perpendicular to plane) = R - 8gcosϴ = 0.
R = 8gcosϴ

After you've done the other equations, try and make simultaneous equations with the expressions you found to try and find ϴ.

I'm not very good at explaining things, but I hope this is of any help to you. ^-^
(please ignore the duplicate of the diagram below - I've no idea why that's appearing)
Attached Images

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