- #1

#### 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?