a chair of mass m sitting on a rough horizontal surface requires a force F appli

Question

a chair of mass m sitting on a rough horizontal surface requires a force F applied in a horizontal direction to cause it to slide at constant speed. If a person of mass M sits in the chair, what horizontal force F' is now required to slide the person and chair at constant speed?

a) F'=(M+m)g

b)F'=Mg

c)F'=(M/m)F

d)F'=[1+(M/m)]F

e)none of the above

We have the answer as C and a very complicated explansion of how to solve this. Its over my head and i would like someone to explain this as detailed as possible... kinda like your trying to explain it to a 4th grader... (hehe)

Explanation / Answer

mass of chair = m

norma force N = mg

friction force = u.N = u.mg ( u- friction coeefificient)

to slide at constant speed   friction force   = F

F = u.mg

so u = F/mg   ..... i)

now with person total mass= (M +m)

norma force N = (M +m)g

friction force = u.N = u.(M +m)g ( u- friction coeefificient)

to slide at constant speed   friction force   = F'

F' = u.(M +m)g

put here value of u   from (i)

F' = F(M +m) / m      anser would be d.

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