9. -1 points OSColPhys2016 8.7.WA.057 My Notes Ask Your Teacher A child is sitti
ID: 1863825 • Letter: 9
Question
9. -1 points OSColPhys2016 8.7.WA.057 My Notes Ask Your Teacher A child is sitting on a stationary skateboard with a pile of rocks which she throws in one direction in order to make the skateboard travel in the opposite direction. If the rocks each have a mass of 0.65 kg and she can throw them with a speed of 16 m/s relative to the ground, determine the number of rocks she must throw per minute in order to maintain a constant average speed against a 3.5 N force of friction. (Note: because this is a rate, the answer may not be a whole number.) rocks/minExplanation / Answer
Given,
Mass of rock, m = 0.65 kg
velocity, v = 16 m/s
force, F = 3.5 N
let m be the mass she is throwing per second
mv = F
m = F/v = 3.5/16 = 0.2188 kg
total mass thrown in one minute = 60*m = 13.128 kg
number of stones = 13.128/0.65 = 20.20 rocks/min
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