Free fall motion

[ozzi22]

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:

A) 0 N
B) 10 N
C) 100 N
D) 200 N

I seriously don't understand why the answer is D. Shouldn't C be the answer? any help will be much appreciated. Thanks.

---

Members don't see this ad.

 

[milski]

If you apply 100 N upwards the net force on the object will be 0 and there will be no acceleration at all. Since they want you to have the same acceleration as in free fall, you want the same net force as magnitude but pointed in the opposite direction, thus you need 200 N up to have a net force of 100 N up.

 

[daFendi]

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:

A) 0 N
B) 10 N
C) 100 N
D) 200 N

I seriously don't understand why the answer is D. Shouldn't C be the answer? any help will be much appreciated. Thanks.

because the question says to SLOW the mass at an equal rate. if you applied 100N upward, there is no acceleration, and the object continues at its current speed. you dont even need to think about the semantics of 'slowing at a rate equal to magnitude G' all you need is Slowing. 100N is already on it, need >100N to slow it. answer is D.