for number 2 i'd say D.

for instance, if they were both spheres, they'd both reach terminal velocity at the same time. if however they had an odd shape, depending on how each object fell (perhaps they were turning as they were falling, exposing a side that would have more surface area and increase drag) one might reach terminal velocity sooner than the other.

So, without knowing the exact shape of the objects and thereby, not knowing how they would behave against air when dropped, you don't have enough information.

-edit:

you could also say 2 is D because the question doesn't clarify if this is taking place in a vacuum or not.

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Last edited by kadomony on Dec-17-2006 at 14:07

Yes, cross sectional area can also have an effect on the drag - but for the purposes of what is clearly someone doing physics in first school here, I think that's being a little bit pedantic.

quote:

Originally posted by DJ Mikey Mike Yes, cross sectional area can also have an effect on the drag - but for the purposes of what is clearly someone doing physics in first school here, I think that's being a little bit pedantic.

Just edited it for a quick and to-the-point answer.

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I'd Say CCB.

1, C - Sunlight contains every wavelength in the spectrum, there for will difract (bend) more than a flashlight would.

2, C - Same shaped objects, e.g. 2 balls one made of steel the other wood, would fall at tidentical rate and hit terminal velocity at the same time. Reguardless if they are in a vacuum or not, the vacuum only comes into play when air resistance is a factor. Since both object are the same shape, they both have same aerodynamics so air resistance is the same for both.

3, B - As the ball climbs into the air, more air molecules will be resisting its climb, as it has to push through the air to rise up. It will displace molecule below it creating the slip stream effect.

I agree it is worded awkwardly too, but from the choices it will have more velocity underneath it.

quote:

Originally posted by Lunar Phase 7 Since both object are the same shape, they both have same aerodynamics so air resistance is the same for both.

Okay, scrap my post - I hadn't read this part of the question. I'll just be leaving now.

"there is ______ velocity under the ball than there is at the bottom."

If there's something is at the bottom of the ball, isn't it under it?!

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There is not enough information for number 2

If it was a vacuum, they would reach it at the same time. But the key thing is air resistance.

Your question never talks about that. IF there was resistance, the bigger object would hit terminal velocity later than the smaller one.

"Once the upward force of air resistance upon an object is large enough to balance the downward force of gravity (9,8m/s^2), the object is said to have reached a terminal velocity."

quote:

Originally posted by SuPeRSaW2005 1) Which light spreads out most (or fastest)(not sure which makes more sense)? a) laser light b) flashlight light c) sunlight

I think the answer is (C). By it's very nature, the laser is a highly coherent source, and hence it's least likely to spread out. The flash light is directional, because the only direction it comes out is from the front of the flash case. There is no directionality to the sunlight since it is emitted in all 360 degrees.

Spread could also mean the spread over electromagnetic wave spectrum. Even from this point of view, sun emits radiation over the entire spectrum from gamma-rays to visible light to radio waves. Suffice to say, it has the maximum "spread". The waves emitted by a flashlight depend on the material properties of the high resistance filament which heats up and emits light when connected to a voltage source. Hence the "spread" is fairly narrow and limited to a part of the visible light and the infrared. Laser is monochromatic (single wavelength), hence it has the least "spread". Either way, sunlight seems to be the correct answer.

quote:

2) Two objects, object A and B, free fall together from a high altitude. Assume Object A weighs less and both object A and object B have the same shape. Which object will reach terminal velocity quicker? a) Object A b) Object B c) Both at same time d) Not enough information

I think the answer is (a) object A . The terminal velocity is reached when the drag forces equal the force of gravity. For a heavier object, the force of gravity is significantly more than the lighter object (assuming they are of the same shape and size) and hence requires higher drag force to balance out the gravity. Now the drag force depends on the velocity of the object, and hence to generate larger drag forces, the heavier body needs to speed up more. As a result, it takes more time to reach the terminal velocity. So in a sense, the lighter object pwns the heavier one when it comes to reaching the terminal velocity quickly

quote:

3) If you throw a baseball up to the sky, there is ________ air pressure at the bottom of the ball than at the top of it, which means there is ______ velocity under the ball than there is at the bottom. a) more, less b) less, more c) more, more d) less, less

I'm thinking the answer is B. Technically, the air pressures on the top of the baseball will be less than the bottom, because air pressure dips as one moves away from the surface of earth. But practically, a baseball thrown up in the air is still very much near to the surface and really too small to take these pressure differences into account.

As the baseball moves through the air, the air pressure in the direction of motion is more than on the other side. Locally, the air molecules get compressed at the top and they create higher pressure in comparison to the pressure at the bottom. A small pocket of low pressure in the bottom of the baseball will be quickly filled in by the surrounding air, and this will result in higher velocities at the bottom.

*disclaimer* I could be wrong on all three questions. Get it double checked with someone else. Physics is kinda hard and you need to think a lot. I might not have taken some factors into account, and I could also be conceptually wrong.

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Last edited by Omega_M on Dec-17-2006 at 16:05

quote:

Originally posted by SuPeRSaW2005 I have a big physics examination coming up, very basic, introductory physics...any physics pros in here that can help me answer these few questions? 1) Which light spreads out most (or fastest)(not sure which makes more sense)? a) laser light b) flashlight light c) sunlight 2) Two objects, object A and B, free fall together from a high altitude. Assume Object A weighs less and both object A and object B have the same shape. Which object will reach terminal velocity quicker? a) Object A b) Object B c) Both at same time d) Not enough information 3) If you throw a baseball up to the sky, there is ________ air pressure at the bottom of the ball than at the top of it, which means there is ______ velocity under the ball than there is at the bottom. a) more, less b) less, more c) more, more d) less, less Any one sure about any of these? Thanks in advance

C
A
?

Okay,

Question 1.

Is about Defraction, where a lightwave "bends", laser light can defract, but not much.

A tourch would defract more, but sunlight even more so for the simple fact it contains all wavelengths of the electromagnetic spectrum, including all ranges of visable light, so no matter how you're going about the bending, it will always bend more than a tourch whihc is at best producing a whitish sorta light.

Question 2.

Both objects = Same shape so air resistance is not a deciding factor. So all this vacuum talk is bollocks. They both hit terminal velocity at the same time.

quote:

Originally posted by Lunar Phase 7 Both objects = Same shape so air resistance is not a deciding factor. So all this vacuum talk is bollocks. They both hit terminal velocity at the same time.

nu uh. weight is the determining factor. if I drop a piece of paper and a piece of sheet metal, both the same dimension, you're telling me they'll reach terminal velocity at the same time?

I DARESAY THE PARTICULARS OF SAID SHAPES AND THE VERY ENVIRONMENT IN WHICH THEY ARE CONTAINED ARE THE DECIDING FACTORS.

BAH!

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