AQA M2 Work done by a variable force

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Can't comment about what's on the syllabus or how it's changed, but they're both doable with work you've covered in other areas I think.

3c.

When v is a maximum, so is 20v^2. So you're interested in the max of that quadratic in part a). I.e. find the stationary point.


5biii).

Is an application of F=ma.

I get q 3 but I wouldn't have thought of it without your prompt so thanks.

But for question 5, what force? I've worked backwards from the answer and still can't work out which force. There's the force of gravity from top to end of cord, then there's the variable force between the end of the cord and the stationary point and then there's the tension force at the bottom. Is that right? I don't get the real life of this do I. I don't know how to think.

You're only interested in the forces acting on the bungee jumper at the particular point found in bii).

Weight acting downwards.
Tension in cord acting upwards.

The variable force in the cord that increases over time until max x, doesn't come into it.

Edit: Experiment:
Tie a weight (sufficiently heavy to stretch the elastic when hanging in equilibrium) to a piece of elastic. Hold the other end of the elastic in your hand and the weight with it. Now drop the weight. That's what's happening with the bungee jumper.