OCR Physics A - G481 Mechanics - [13/01/09][@1400]

OH MY GOD projectiles
i hate projectiles

never know what to do!!!!

Reply 81

neomilan

OH MY GOD projectiles
i hate projectiles

never know what to do!!!!

I think it's best to look at the vertical and horizontal bit seperately. Sometimes they give you a the velocity at an angle and you have to resolve it and sometimes they just give you the horizontal part and or vertical.Use SUAT on the vertical taking a as gravity so 9.81 and use speed= distance/time for the horizontal part.

Reply 82

annaroberts20

That carriage question sucked big time!!! Usually you would use the simple equation when they want average speed or average velocity or when the velocity is constant whereas u would use SUVAT when there is constant acceleration so changing velocity and on projectiles remember you only SUVAT on the vertical bit and then the simple equation on the horizontal bit

Oh ok, thanks a lot for that, was just using blind guessing before. Projectile motion isn't that bad, just that horizontal is always constant and acceleration is always 9.81.

Reply 83

Ah i see what happened just now, the two threads were merged!

Anyway, back to physics:
can someone explain how the measuring G experiment works... light gates thingy?

Thanks

Reply 84

What I think it is, is its a metal ball held with a clamp thing above a light gate and another catcher thing at the bottom (sorry for these casual words :p:

)
When the ball is released the time starts and the speed is calculated as it passes the light gate, once it hits the ground, the timer is stopped :smile:

Reply 85

beesbees

neomilan

Ah i see what happened just now, the two threads were merged!

Anyway, back to physics:
can someone explain how the measuring G experiment works... light gates thingy?

Thanks

Basically you have a card of a length. (say, 5cm). Then you have two light gates at a set distance apart (eg, 1m). You then have the first light gate above the other, and drop the card through them.

The light gate will measure how long it was broken for, so using speed = distance divided by time you can work out the speed through each light gate.

Then applying this to v^2 = u^2 + 2as, you can work out the acceleration, where U = speed at first light gate, and V = speed at second light gate.

Cos it's in free fall, a = g :smile:

Reply 86

beesbees

Can also use a ball held by an electromagnet. You turn on the switch and the ball is released and the timer is starter. When the ball goes through the trapdoor at the bottom, the circuit is broken and the timer stops. You would have measured the distance form the bottom of the ball to the top of the trapdoor and now you have the time so you can use S=ut+0.5atsquared
And putting the numbers you will be left weith half of gravity times t squared.

Reply 87

Can someone clarify this for me please??
I know that if you ignore air resistance, during free fall, the mass of an object does not affect the acceleration as the acceleration would always be equal to gravity.

But if you have horizontal acceleration like with a car, does the mass affect th acceleration? Cause if you look at F=ma and if you have the same force with a small mass, you have a bigger acceleration and vice versa.

Have I got this theory right?

Reply 88

annaroberts20

small mass = larger acceleration
larger mass = smaller accelleration
at constant force

Reply 89

neomilan

small mass = larger acceleration
larger mass = smaller accelleration
at constant force

But am I right that it doesn't apply to acceleration of free fall?

Reply 90

annaroberts20

But am I right that it doesn't apply to acceleration of free fall?

if an object is in free fall, the only force acting on it is gravity, therefore its acceleration is equal to g

if there is another force acting on it, such as air resistance then it will be different

with that car you mentioned, i believe that since the car has a force (engine force) then its acceleration will change ... whereas a ball just allowed to free fall does not have forces added to it so its accelereation will be the same as G

Reply 91

-G-a-v-

neomilan

Ah i see what happened just now, the two threads were merged!

Anyway, back to physics:
can someone explain how the measuring G experiment works... light gates thingy?

Thanks

Make sure you write acceleration due to gravity as g not G - G is the gravitational constant.

Reply 92

-G-a-v-

Make sure you write acceleration due to gravity as g not G - G is the gravitational constant.

ah yeah, i knew that i don't know why i wrote it as G instead of g

erm, seeing as you're a physics degree student, can you verifiy if what i said is correct in terms of annaroberts's question

neomilan

annaroberts20

But am I right that it doesn't apply to acceleration of free fall?

Reply 93

Spongebob*No*Pants

According to the spcimen data sheet for 2008 Physics A

it says:

"The information in this sheet is for the use of candidates following
GCE Physics A H158 and H558.
Clean copies of this booklet must be available in the examination room, and must
be given up to the invigilator at the end of the examination.
Copies of this sheet may be used for teaching"

These forumlas will be given in the exam!

F cos (theta)
F Sin (theta)

a= delta V/ delta T

the 4 suvat equations

F=ma

moment = fx

Torque = fd

press. = F/A

Dens. = M/V

K.E = 1/2 mv^2

P.E = mgh

efficiency

stress

strain

and young modulus

Reply 94

DrVas

Spongebob*No*Pants

They may as Well give you the Mark Scheme as well.

Reply 95

Spongebob*No*Pants

Haha, wtf??
That is indeed pretty much giving you about 50% on the paper already, because I am 100% sure you get 1 mark for writing an equation down, so it makes it a little easy doesn't it??

I spent AGES revising and memorising these equations and they just go ahead and give it to us!?!?!? :eyeball:

Reply 96

DrVas

dave2k

I HAD TO AND HAVE LEARNED ALL THE EQUATONS, and the ones for A2 as well.

and the New Spec comes along, and give you the formulas, they must think that you are REALLY stupid.

Reply 97