TranceAddict Forums (www.tranceaddict.com/forums)
- Chill Out Room
-- Conceptual Physics Question
Pages (3): [1] 2 3 »

Conceptual Physics Question

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

im gonna go with a...not much of a choice there...

EDIT: ok now you put the answers in...

There's a lot of spreading in the Red Light District

EDIT: ok now you put the answers in... but my answer is still correct!

quote:

Originally posted by Lira There's a lot of spreading in the Red Light District

wOOt wOOt!!!

nice one Lira. nice to see a quality post from an old skool TA !

>JM<

B
B
C

quote:

Originally posted by JM wOOt wOOt!!! nice one Lira. nice to see a quality post from an old skool TA ! >JM<

Cheers

im sorry, but do u guys know for sure or are u guys just guessing? because i really need to know this stuff for sure...thanks

quote:

Originally posted by SuPeRSaW2005 im sorry, but do u guys know for sure or are u guys just guessing? because i really need to know this stuff for sure...thanks

1)
B - visible light, in the form of the full specturm [i.e. white light] spreds out more than any color does individually [i.e., the sun]. the laser light is infrared, and does not scatter as much, since it's of a different wavelength.

2)
B - since the objects are not in a vaccum, the heavier object [object B] will reach terminal velocity faster.

3)
C - there is more pressure underneath the ball because pressure decreases with heigh in the atmosphere. the second part of the question is worded awfully awkward. i don't know what they're getting at. but, it has to be either A/C so pick one.

its been awhile since i've had physics like this, but that was the quick and dirtay rationale i had on those questions.

for number 2, when u say object b will reach terminal velocity faster.....


i know for sure that the heavier object (object b) will hit the ground first, but is that the same thing as saying it will reach terminal velocity faster THATS why itll hit the ground first?

quote:

Originally posted by SuPeRSaW2005 im sorry, but do u guys know for sure or are u guys just guessing? because i really need to know this stuff for sure...thanks

you need to know for sure so you ask a message board.

quote:

Originally posted by tubularbills 2) B - since the objects are not in a vaccum, the heavier object [object B] will reach terminal velocity faster.

drop an ant and a buick, see what happens

Re: Conceptual Physics Question

quote:

Originally posted by SuPeRSaW2005 any physics pros in here that can help me answer these few

Yea, because the questions asked here would make even Einstein sit back for a second and say 'hang on, WOAH!'

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.

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.

Re: Conceptual Physics Question

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.

Re: Re: Conceptual Physics Question

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?!

Re: Re: Conceptual Physics Question

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."

Re: Conceptual Physics Question

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.

Re: Conceptual Physics Question

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!

F) Lightshow!

A) Light bends on ma dick

E) Most everyone is familiar with the drop in pitch of a train whistle as a train passes your position and switches from moving toward you to moving away from you. This phenomenon is called the Doppler Effect , and is associated with the wave nature of sound: the relative motion of the source causes the wavelength of the sound waves to be decreased ahead of the source and stretched out behind the source (musically, the pitch of a note is correlated with the wavelength of the corresponding sound wave; thus, the longer the wavelength, the lower the pitch). The droppler of my pooh to the toilet bowl is equivalent to the stretch of your mommas vagina while you were being born. Light also can be described as a wave, and relative motion of the source of light waves leads to a corresponding Doppler effect for light. In this case it is not the pitch but the color (that is, the wavelength) that is shifted by the motion of the source. Now it's time for poopies. The wavelength is shifted to larger values if the motion of the source is away from the observer and to smaller values if the motion is toward the observer. The shift to larger wavelengths by motion away from the observer is called a red shift by astronomers and a shift to shorter wavelengths caused by motion toward the observer is called a blue shift. Lets all let the rat nibble on our rectums. The terminology is borrowed from the visible part of the spectrum where blue is toward the short wavelength end and red is toward the long wavelength end, but the Doppler effect occurs for all wavelengths of light, not just the visible spectrum

Powered by: vBulletin
Copyright © 2000-2021, Jelsoft Enterprises Ltd.