If you wear kneepads when skating, after a fall to your knees it will take 3 times as long for them to come to a rest. how does this affect the change in momentum of your knees during the fall? a. the change in momentum is the same with or without the kneepads b. the change in momentum decreases by a factor of 9 c. the change in momentum decreases by a factor of 3 d. the change in momentum increases by a factor of 3

 
When you fall, you arrive at the floor with some momentum.  It makes
no difference what stops your fall, or how long it takes to stop your fall. 
It still has to absorb the same amount of momentum, somehow.  As long
as your body still has any downward momentum, you're still falling.

The total change in momentum can also be viewed as some amount
of 'impulse' ... the product of force and the time that the force persists. 
The knee pads absorb your momentum slower than the bare floor does,
and since the process of changing your momentum lasts longer, the
corresponding force against your knees is smaller with the pads.

Well it depends on the object or substance