Bob, who has a mass of 75 kg, can throw a 500 g rock with a speed of 30 m/s. The distance through which his hand moves as he accelerates the rock forward from rest until releases it is 1 m.(adsbygoogle = window.adsbygoogle || []).push({});

A) what constant force must Bob exert on the rock to throw it with this speed?

B) if bob is standing on frictionless ice, what is his recoil speed.

I got part A by doing V^2= Vi^2 + 2a(Xf-Xi), where 30=Vf, 0=vi, Xf-Xi= 1. And I got 450 m/s^2 for the acceleration. Then I plugged this in F=ma=.50 * 450= 230 N

I have no idea how to do part B. The only force I see on bob are the normal force and weight and perhaps the force of his legs propelling him back? I'm not sure! Can someone please help guide me for part B?

Thanks!

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# Homework Help: Question about recoil speed

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