The magnitude of the frictional force Fk acting of the object is?

Question

Hello ! Can you please help me?

I know that we determine the frictional force by Fµ = µ * Fn , I can't seem to figure out the friction coeffecient to get the value. The question is :-

The diagram shows a 4 kg object accelerating at 10 m/s^2 on a rough horizontal surface. The magnitude of the frictional force Fk acting on the object is?

This is the diagram: http://bb.tgareed.com/2012/5SA49433.png

The answer is 10 Newton but I don't really know how to get it

Thanks in advance!

Answer 1

By newton's 2nd law,

F(total)=ma

50 - friction = 4*10

-friction = 10

friction = 10 N.



This is what has been posted but it wise to comment on this that the diagram shown we are not aware of the coefficient of kinetic friction. I mean what its value is. So its the only alternative way out. So we continue with a little Physics courage and find the frictional force. In fact it is the method about how we determine the value of coefficient of kinetic friction through experiments for a particular pair of bodies.

Answer 2

BY F(net) = F(applied) - F(friction)

=>ma = 50 - Fk

=>4 x 10 = 50 - Fk

=>Fk= 10 Newton

Answer 3

F(total)=ma

50 - friction = 4*10

-friction = -10

friction = 10 N.

Answer 4

F - Fk = ma = 4*10 = 40 or {Newton's second law}

50 -Fk = 40 or Fk = 10 N