PHYA4 AQA Physics Unit 4 Jan 27th 2011

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Reply 80

SamEmery

Default Re: PHYA4 AQA Physics Unit 4 Jan 27th 2011
i used 1 aswell thats right i though?

Yh alot of people are getting 11? How the hell? I was like 100% sure it was 22 at the time.

Reply 81

Ooo'Yeah

How did people work out 1b, the radius of the Hubble telescope? I sat there thinking for ages thinking it was probably really simple, but in the end just gave up and wrote down a random number so I could get error carried forward for 1c :s-smilie:

Reply 82

Webbykun

Original post by pinfultommy

I got 16 degrees but essentially guessed! How did you work it out?

If you resolved the forces, you'd get something like Tcos(theta) = mg and Tsin(theta) = F where T is the tension in the string and F is the electrostatic force. I think they were the equations I got, can't remember the exam seems ages away :tongue:

.
Tsin(theta)/Tcos(theta) = tan(theta) = F/mg. Something along those lines.

Reply 83

SamEmery

Default Re: PHYA4 AQA Physics Unit 4 Jan 27th 2011
how did you guys work out t did you use V=Voe^-t/RC?

yup!

-ln(V/Vo)RC = t

Reply 84

CitizensUnited

I got 16 degrees for the angle (used trig), I got the impulse on the ball question as 10.

Original post by 88 movement

how did you guys work out t did you use V=Voe^-t/RC?

That's what I did. Did you get 4 and a bit?

Reply 85

Andrea03

Original post by CitizensUnited

I got 16 degrees for the angle (used trig), I got the impulse on the ball question as 10.

That's what I did. Did you get 4 and a bit?

The time was 3.2s.

Reply 86

jontylol

Paper wasnt bad. Only real issue was the impulse one, as i got 15 ish for the final speed. Did you have to take into account the direction of the velocity cos i did

(0.42 * v) - (0.42 * -10) = 10.75

The -10 as v is in the opposite direction to v, and a positive impulse as its in the direction of v.

And for the angle question how did people do it? I ended up using sin/cos=tan but im sure theres a simpler way as you're not required to know that/

(edited 13 years ago)

Reply 87

bl0b

For the angle question this is how I did it:

The forces acting on the object were Tension, Electrostatic Force and Gravity

T sin\theta = F_e

T cos\theta = mg

\frac{T sin\theta}{T cos\theta} = tan\theta

tan\theta = \frac{F_e}{mg}

\theta = arctan \frac{F_e}{mg}

iirc the answer was 14.3 degrees

Reply 88

Andrea03

Im pretty sure each block was 1Ns

Reply 89

88 movement

That's what I did. Did you get 4 and a bit?

I think I made a mistake, I got 0.17 :/

I did mw^2r = GMm/r^2

Reply 90

Webbykun

Original post by jontylol

Paper wasnt bad. Only real issue was the impulse one, as i got 15 ish for the final speed. Did you have to take into account the direction of the velocity cos i did

(0.42 * v) - (0.42 * -10) = 10.75

The -10 as v is in the opposite direction to the 10, and a positive impulse as its in the direction of v.

And for the angle question how did people do it? I ended up using sin/cos=tan but im sure theres a simpler way as you're not required to know that/

Yeah I got same as you, 15ish. Ft = mv - (-mu) = mv + mu. Which makes sense because Ft - mu = mv so if Ft is constant and u increases, the velocity with which the ball is kicked back at will decrease which is what I put as my answer for the next part too :smile:

Reply 91

Webbykun

Original post by bl0b

For the angle question this is how I did it:

The forces acting on the object were Tension, Electrostatic Force and Gravity

T sin\theta = F_e

T cos\theta = mg

\frac{T sin\theta}{T cos\theta} = tan\theta

tan\theta = \frac{F_e}{mg}

\theta = arctan \frac{F_e}{mg}

iirc the answer was 14.3 degrees

That's peculiar because our methods are exact and I got 15.15 degrees which I rounded to 15 (2 s.f).

Reply 92

04cartert

resolve ^ mg = Tcos0
resolve > F = Tsin0

put together F/mg = tan0

comes out as 15.4 i think...

Reply 93

RoroZoro

Original post by m0man

For the very first question on the multiple choice, did anyone else put A? It didnt say anything bout energy being lost

And for the radius of the hubble telescope, did anyone get 6.99x106 or something?
Thanks

I got 6.99x10^6 for that question ^^