You are Here: Home >< Physics

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

1. OH MY GOD projectiles
i hate projectiles

never know what to do!!!!
2. (Original post by 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.
3. (Original post by 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.
4. 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
5. 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 )
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
6. (Original post by 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
7. (Original post by beesbees)
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
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.
8. 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?
9. (Original post by annaroberts20)
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?
small mass = larger acceleration
larger mass = smaller accelleration
at constant force
10. (Original post by 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?
11. (Original post by 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
12. (Original post by 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.
13. (Original post by -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

(Original post by neomilan)
(Original post by 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
14. 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
15. (Original post by 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

They may as Well give you the Mark Scheme as well.
16. (Original post by 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!
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!?!?!?
17. (Original post by dave2k)
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!?!?!?

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.
18. Hehe, this has given me some hope that the paper will be simple!!

19. (Original post by dave2k)
Hehe, this has given me some hope that the paper will be simple!!

"Define Young's Modulus, (ahh forget it Here is two marks)"

Or THEY WILL RAPE YOU, with DIGUSTINGLY Hard questions.
20. Whaat? That's just ridiculous!

They're not exactly hard to remember for this paper, anyway, are they? I've put hardly any effort into memorising them, but by just doing past papers you just get to know what they are.

Updated: May 9, 2014
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Grade boundaries not out until results day

What does this mean for you?

Poll
Useful resources