An adventurous camper (70 kg) finds him/her self stranded in the middle of a fro

Question

An adventurous camper (70 kg) finds him/her self stranded in the middle of a frozen lake (diameter = 1.1 km) with only a bag of rocks (total mass 13.0 kg). The ice is so slippery, that they move about the lake's surface without friction (don't ask me how they got there in the first place). Remembering what they learned in a physics lab, they devise a way to get themselves to the edge of the lake by throwing the bag of rocks in the opposite direction of the shore with a velocity of 3.0 m/s. If they throw the rocks all at once, how long does it take for them to slide to shore?

Explanation / Answer

Momentum is conserved.
momentum given to rocks is 3 * 13 = 39kg m/s

The same momentum ( but opposite direction ) is given to the camper.
hence 70 * v = 39
v = 39 / 70 m/s
D=1.1km therefore r=550m
If v = d/t
then t = d / v = 550/( 39/70) = 987 s
You might have gone faster to hold your jacket up and let the wind blow you to the other shore.

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