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pitbull

a ball of mass 0.500kg is attached to the end of a cord 1.50m long, the ball is whirled horizontaly on a friction less table, if the cord can withstand mass of 10.0kg a) what's speed of the ball.

i used Fr = mar = m(v^2/r)

i solved T max = m(v^2/r) *T max -

v = square root Tr/m

= (10.0*1.50m)/0.500kg

= 5.6m/s

now this is the max speed the ball can have before the string breaks, however they asked for the speed not the max it can take before the string breaks ??? are these two the same speed = max speed if not can someone show me.

another question:

a 1000kg car accelerates uniformly to speed of 30m/s in it's first 10s find a)work done on car in this time b)avg power delivered c)instantaneous power delivered by engine at t = 2s.

W= Kf-Ki

W= 1/2mvf^2- 1/2mvi^2 = 1/2m(vf^2-vi^2)

a) 450000 Jules

b)P = W/T = 450000/10s = 45000 Watts

c) instantaneous ???? how?