Question

A box of mass 8 kg sits on a horizontal
tabletop. An unstretched spring of force con-
stant 420 N/m runs between the box and a
wall. The coefficient of friction between box
and table is
1
2
. Another box of mass 10 kg
is hung from a string of negligible mass tied
to the front of box 1, and allowed to fall from
rest.
420 N/m
8 kg
10 kg
`
`
μ = 0.5
By what amount has the spring has been
stretched when the acceleration of the boxes
has magnitude 1 m/s2? Assume gravitational
acceleration is 10 m/s2.
Answer in units of m