Homework Help: Mass Free Fall

A 10 kg mass is in free fall with no air resistance. In order to slow the mass at a rate equal to the magnitude of g, an upward force must be applied with magnitude:


F=ma



F=(10kg)(9.81m/s2) = approximately 100N

So in order to slow the mass at a rate equal to g it should be a force less than 100N?? Im not sure how to figure this out. Help!!!

Thanks

Jerry Zink

 

The two forces are

1. gravitational force on the 10kg mass "going down"
2. The upward force "going up"

So the upward force must go against the force of gravity plus the force of the mass.

The mass has a force of F=ma = 100N downward

Since the upward force is in the opposite direction it has to counteract the downward force and slow it down to = g

Im just having trouble formulating the expression for the upward force.

 

Would the upward force be :

F=m2a ?

F=(10kg)(2)(9.81m/s2) = 196N

is this correct?

 

The resultant force should be in the upward direction

 

OH! So the resultant force is in the downward direction.

 

so W = ma + u

a = 9.81m/s2

so W is equal to the downward force of 100N?

So this means u = W - ma

U = 100N - (10kg)(9.81m/s2)

U = 1.9N

Is this right?

Are you sure its not this "ma = U-W"

This would make more sense because then U is = to around 200N

 

Is the resultant force still the force of the mass 100N downwards?

 

?? So if the resultant force is zero how do we find the upward force?

 

So if the upward force is equal to the downward force W=U

Fw = (10kg)(9.81m/s2)

W = 100N
U = 100N

This doesnt seem right?

 

Then wouldn't that implicate that the mass is not moving?

 

That makes sense, but the answer in my book says the upward force is equal to 200N. This is what is throwing me off. Maybe the book is wrong.

I really appreciate your help rock.freak667

Can you make any sense of the 200N answer?

Thanks again

Jerry Zink