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Physics: Post your doubts here!

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2(D) Use s=ut + 1/2 at^2. Sub in time from c(ii) and acceleration from c(i). Your answer should be s=12.71cm. But the length of the metal plates is only 12cm. Since s calculated is longer than metal plates, electron will emerge from plates.

5(c) I'm not so sure. My answer for you would be from the marking scheme so if you're looking for explanation, it wouldn't be helpful..
 
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Hi everyone :)
Can anyone help me find a website where I can find classified pastpapers ??
 
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Can anyone help clarify? For Q4, why is the answer D not B? For Q10, Why is it not A but D? Thanks!! :)
 

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Does anyone has an idea about the physics practical where we don't have to draw any graph?
 
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Can anyone help clarify? For Q4, why is the answer D not B? For Q10, Why is it not A but D? Thanks!! :)
For Q no. 4 the total range with which the values are fluctuating is +- 0.04 not +- 0.02 . So the range is +- 0.04. That's my reason . And for question no. 10 we know that in case of elastic collision u1 - u2 = v2 - v1 ( i.e Speed of approach = Speed of separation ) . Since the body are initially travelling in opposite direction so one velocity must be in negative direction. Since u1, v1 and v2 are in same direction so it is better to take u2 as negative ( But you can alter that and take u2 as positive and others as negative. You will end up with the same answer in either case. ) Now since u2 is negative so the above eqn. becomes (u1 + u2 = v2 - v1 ) So D not A. I guess you are clear now. (y)
 
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Does anyone has an idea about the physics practical where we don't have to draw any graph?
Yes for the question no. 2 of Paper 3 . You have to write the errors and ways to solve them and you usually don't have to draw graph in those questions.
 
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For Q no. 4 the total range with which the values are fluctuating is +- 0.04 not +- 0.02 . So the range is +- 0.04. That's my reason . And for question no. 10 we know that in case of elastic collision u1 - u2 = v2 - v1 ( i.e Speed of approach = Speed of separation ) . Since the body are initially travelling in opposite direction so one velocity must be in negative direction. Since u1, v1 and v2 are in same direction so it is better to take u2 as negative ( But you can alter that and take u2 as positive and others as negative. You will end up with the same answer in either case. ) Now since u2 is negative so the above eqn. becomes (u1 + u2 = v2 - v1 ) So D not A. I guess you are clear now. (y)
Thank you soo much :D
 
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For Q no. 4 the total range with which the values are fluctuating is +- 0.04 not +- 0.02 . So the range is +- 0.04. That's my reason . And for question no. 10 we know that in case of elastic collision u1 - u2 = v2 - v1 ( i.e Speed of approach = Speed of separation ) . Since the body are initially travelling in opposite direction so one velocity must be in negative direction. Since u1, v1 and v2 are in same direction so it is better to take u2 as negative ( But you can alter that and take u2 as positive and others as negative. You will end up with the same answer in either case. ) Now since u2 is negative so the above eqn. becomes (u1 + u2 = v2 - v1 ) So D not A. I guess you are clear now. (y)

Oh, I forgot to ask. For speed of approach=speed of separation, the formula is u1-u2 = v2-v1 right? As you showed previously.. So I can't use m1u1 + m2u2 = m1v1 + m2v2 ?
 
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Tobi will help you solve it! :D
Alright
u = 10 m/s
v = 0 m/s
s = 10 m

That's the first case
So...
You gotta find the retardation of the car first [Basically negative acceleration]
So....
Yeah
* = Multiply

V*V = U*U - 2*a*s
0 = 100 - 20a
-100 = -20a
a = 100/20 =( 5m/s*s)

That's the acceleration of your car! CAR FTW ! XD

Now the question is IF he were to travel at 30m/s,what'd be the distance


Therefore use the same equation again nacho :D

But in this case:
u = 30 m/s
v = 0m/s
s = ??? m
a = 5 m/s*s


V*V = U*U - 2*a*s
0 = 30*30 - 2*5*s
0 = 900 - 10s
- 900 = -10s
s = -900/-10 = 90m

90m OMG. That's the answer lol xD


btw doesn't a motorist drive a motorcycle instead of a car?How can a biker drive a car at the same time when he's driving a bike?:/
haha, no the motorist drives a vehicle powered by a motor,here, a car:)
 
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Oh, I forgot to ask. For speed of approach=speed of separation, the formula is u1-u2 = v2-v1 right? As you showed previously.. So I can't use m1u1 + m2u2 = m1v1 + m2v2 ?
Its not for elastic collision. That's for inelastic collision. In case of elastic collision the kinetic energy of the body is conserved so we have to use the another equation that I mentioned earlier. I guess you are clear now. :)
 
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For Q1, cube root 2.7 x 10 ^ 25 m ^-3 and you get 6.46 x 10^-9 m. Divide the answer by two again and you get the final answer. I don't know why divide by two though...
For Q2, use P1/T1 =P2/T2 to get the pressure when box is 200 degree celsius. Remember that temp should be in Kelvin. You should get 1.65 x 10^ 5 Pa. Since it says net force, find its net pressure. Outside the box there's atmospheric pressure of 1.01 x 10^5 Pa already. Inside the box, there's 1.65 x 10^5 Pa. So minus that and you get 6.5 x 10^4 Pa. That times the area which is 0.09m squared, you'll get the final answer :)

Heyyyyy!! Thanks loads ! :)
 
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Resolve v :
1. You get v cos theta along X . So magnitude of X = v cos theta
But using mathematical knowledge :
Increasing theta form 0 to 90 degrees causes cos theta to decrease . Remember the graph for cos theta ? Do refer to it.
Hence along X , v cos theta decreases, so X decreases.

2. You get v sin theta along Y .So magnitude of Y = v sin theta .
But again applying mathematics:
Increasing theta from 0 to 90 degrees causes sin theta to increase . Refer graph of sin theta .
Hence Y increases.

Hope it helped!
 
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Can someone please help me out with this?

A beam of monochromatic light of wavelength 630 nm transports energy at the rate of 0.25 mW. Calculate the number of photons passing a given cross section ina given second.

Answer is 8*10^14
 
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When a ball is dropped and allowed to fall under free gravity it will have three different stages- initially the resistance will greatly oppose the body, so the displacement/time graph would NOT be too steep but would (obviously) have a negative gradient. Then eventually, the ball will reach terminal velocity, where acceleration is 0 and the speed is constant, so you will get a straight line with a negative gradient. Then, finally will come a point where when the downward force will be much greater than the resistance (when it gets closer to the ground), hence the graph will be VERY steep.

From the description you can tell the answer is B. :)
 
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Could anyone explain to me how to solve this question briefly??
Thanx in advance...
 

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Its not for elastic collision. That's for inelastic collision. In case of elastic collision the kinetic energy of the body is conserved so we have to use the another equation that I mentioned earlier. I guess you are clear now. :)
thanks!
 
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