Question

A body initially at rest is acted upon by a constant force of 18lb for 5 sec, after which an opposite force of 12lb id applied. In what additional time will the body come to rest

Answer 1

initial force F₁ =18 lb=80 N

initialaccelertn a₁ = $80\over m$

final velocity before second force applied will be

$v=u +at$

$v=0+{80\over m}t ={80\over m}\times 5={400\over m}$

now opposite force F₂ =12lb=53.37 N is applied

and final velocity is 0.

$0={400\over m}-{53.37\over m}t$

we get t=7.5 sec.