Question

A block is pulled horizontally across the rough surface of a table by means of a spring scale at constant speed. The reading on the spring scale is 14N .the pulling force is now increased to 31N and the block experiences an acceleration of 8,5m's squared calculate the friction between the block and the table surface

Answer 1

block mass = m
weight = m g
normal force on surface = m g
friction force = mu m g = 14N given so mu = 14/mg
31 - 14 = m a
17 = m a = 8.5 m given
so m = 17/8.5 = 2
mu = 14/2g = 14 /[2 g]
= 14 / 20
if g = 10 then mu = 0.7

Answer 2

14-Ff = M*a.
14-Ff = M*0 = 0,
Ff = 14N. = force of friction.