Question

A spring (k = 29.5 N/cm) is attached to a block of mass m = 8 kg.
The block rests on a surface and the coefficients of friction between the block and the surface are μs = 0.6 and μk = 0.3 respectively.
The spring is unstretched at this moment.
A force F is then applied to the end of the spring opposite the block.
(a) At what value of the force F will the block begin to slide?
(b) By how many centimeters will the spring be extended at this "first motion" point?
(c) If the stretch of the spring is maintained at this value, what will be the acceleration of the block?

Answer 1

(d) How fast will the block be moving when it has been pulled a distance of 1.2 meters after it first starts to slide?

Answer 2

a)
F = us*m*g
b)
extension (in cm) = F/29.5
c)
Total force on block = m*a
Total force = spring pulling + kinetic friction
total Force = us*m*g- uk*m*g
us*m*g- uk*m*g = m*a
us*g-uk*g = a

Answer 3

d)
The spring can only push the block 0.8 cm.... As at this moment the kinetic drag brings it to a halt.