A light spring with force constant 3.75 N / m is compressed by 8.32 cm as it is

Question

A light spring with force constant 3.75 N / m is compressed by 8.32 cm as it is held between a 0.251 kg block on the left and a 0.502 kg block on the right, both resting on a horizontal surface. The spring exerts a force on each block, tending to push them apart. The blocks are simultaneously released from rest. Find the acceleration with which each block starts to move, given that the coefficient of kinetic friction between each block and the surface is the following values. (Let the coordinate system be positive to the right and negative to the left. Be sure to include the sign to indicate the direction of the acceleration.) mu = 0 heavier block Your response is off by a multiple of ten. m / s2 lighter block The response you submitted has the wrong sign, m / s2 mu = 0.070 heavier block Consider carefully whether the correct answer is exactly zero, or just a very small number, m / s2 lighter block The correct answer is not zero, m / s2 mu = 0.147 heavier block m / s2 lighter block m / s2

Explanation / Answer

a) no friction so F = kx so a = kx/m light block: a= 3.75*8.32E-2/.251=1.24 heavier block: a= 3.75*8.32E-2/.502=0.622 b) now there is friction so F = kx - friction = kx - u m g so a = F/m a = k/mx - ug lighter block a = 1.24 - 0.07*9.81=.553 heavier block a= .622-0.07*9.81= -0.0647!! This can't be!! but this makes no sense since friction can't make you go opposite way so a=0

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