Homer Simpson (250lb) is suspended initially in perfect balance with a bag of donuts?

Question

Every 10 seconds Homer reaches into the bag, retrieves one donut (1/2 lb), and consumes it.

What is the magnitude of the jerk?

http://alexandersemenov.tripod.com/ya/jrk/index.htm



The rope and the block are weightless and frictionless.

Answer 1

Jerk is the change in acceleration. Since the transfer yields a net increase of 1lb (Homer increases 1/2lb, the bag decreases by 1/2 lb).

Pounds are force, and the force acts on the net mass of 500 slugs.

Δa = 1 lb / 500 slug
jerk = Δa/t = 1 lb / 500 slug / 10 s
jerk = Δa/t = 1/5,000 lb / slug s

Answer 2

I don't see how the 10 second interval enters into it. (In the picture, Homer has retrieved a donut and is spending the rest of the 10 sec nibbling it, which does not affect the acceleration.) So how long (what dt) does the act of donut retrieval (weight transfer) take? The jerk is (1 lb / 500 slug) / dt ft/sec^3.

Answer 3

Homer Simpson is not real. Therefore the magnitude of the jerk is 0.