Question

A 60 kg body is pushed horizontally with just enough force to start it moving across a floor and the same force continues to act afterwards. the coefficient of static friction and sliding friction are 0.5 and 0.4 respectively. the acceleration of the body is

Answer 1

Thank you for asking the question
As we know that static friction =  coefficient of static friction *  normal reaction of the body
that is friction = (u)N 
also N=(m)(g) =60* 10  = 600 N ( By just taking g= 10 m/s^2
static friction = 0.5 * 600 = 300 N
when the external force will be applied on body .it will be start moving so in this case kinetic friction= 0.4 * 600 = 240 N

so the net force will be difference of both type of friction = 300- 240 = 60 N
we know that
F= ma so 
a=F/m
so by butting values 60/60 =1 m/s^2 (acceleration).

Answer 2

Answer:

Explanation: acceleration = coefficient of friction * gravity

body just begins to slide so there is no static friction so there is limiting friction so acceleration = 0.4*9.8

= 3.92 meters  / second ^ 2