Quote:
Originally Posted by headlight
He might be trying to think of it from a terminal velocity perspective. The heavy rock will have a faster terminal velocity, the lighter rock will have a slower terminal velocity. So it would seem intuitive that the lighter rock is encountering more resistance because it is going slower (even though it is the heavier rock that actually has a greater force being applied to it by the air).
Overall it seems to be a poorly worded question, a more clear question would be to ask which experiences greater drag force due to air resistance.
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And drag force is affected by both surface area and velocity.
If you put together a free body diagram, you may be able to solve this one out. Gravity is acting downwards (9.8m/s^2 * Mh for the heavy rock, 9.8m/s^2 * Ml for the light rock), drag force is acting upwards (I don't have a formula handy, but it's a function of velocity and surface area, and varies depending on shape--thankfully, rocks tend to be approximated "nicely" with a sphere).
Now all you have to do is determine which one needs a greater drag force to have Fgravity = Fdrag, and then you can determine things like which one is falling faster...
But, in this case, it's the heavy one (Mh is by definition > Ml). The EFFECT of the air resistance is seen most on the light one (Fdrag needing to be smaller on a body that is to all intents and purposes the same surface area but less massive in order to counter Fgravity).
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