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AQA June 2011 Mechanics 1B 26th May

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Reply 80

nadya18

did anyone get something like 80.4 or 80.3 for h on projectiles question?

Reply 81

Miller693

Original post by nadya18

did anyone get something like 80.4 or 80.3 for h on projectiles question?

Think I got 78.4 :s-smilie:

Reply 82

Joshp93

Original post by nadya18

did anyone get something like 80.4 or 80.3 for h on projectiles question?

Do you remember the time it took to hit the floor? Cos then i can work it out as i can't seem to remember what i got.

And 78.4 wasn't my height but my tension on another question :s

Reply 83

ezeffy

its kinda clearer now.. thnx..... but i thought that it had stopped accelerating so i let a=0 and then I i used r=ut.....
the s they gave us was distance so i squared it so that it became 500^2... 250000 therfore....
250000=(ut)^2 and then whateva V was becomes U (it seemed logistic at the time.. lol.....) and then my final answer came out as 28.7 or something lyk that.......
now i know that completly wrong..... sooooooooo annoyed......

Reply 84

nadya18

Original post by Joshp93

Do you remember the time it took to hit the floor? Cos then i can work it out as i can't seem to remember what i got.

And 78.4 wasn't my height but my tension on another question :s

i think t=4

Reply 85

Miller693

Original post by Joshp93

Do you remember the time it took to hit the floor? Cos then i can work it out as i can't seem to remember what i got.

And 78.4 wasn't my height but my tension on another question :s

Ok maybe it was a tension, saying that, you've put doubt in my mind. Ah well.

Reply 86

Joshp93

Original post by ezeffy

Damn :/ yea was a silly mistake, yet it ends up losing you 5 marks :/ and its not something they can do an ECF for since you would of got wrong answers and wrong methods springy up everywhere if you assumed it stoped acclerating, best thing to do is not to assume anything. Except when you are talking of air resistance etc. :smile:

Reply 87

seejay1

Original post by Joshp93

Really can't understand how so many people struggled with this...
They give you acceleration, they say the helicopter starts from rest (u=0ms-1) they give you a distance. So all you do is find the magnitude of the acceleration, and then whack it into s=ut+0.5at^2 and out comes t^2=1600 so t=40s.
I think the reason is because people dont realise its just the magnitude that they need. I think i must of used the magnitude about 4 times in this paper and s=ut+0.5at^2 about 5 or 6 times lol.

Your right! Thats what I think is a bit silly. Although I was fine, anyone who didn't know that equation was in the **** :tongue:

Was it 0.2ms-2? or maybe 0.4 but the weight were 5kg and 3kg. I was wondering in the exam, that if you have two things connected, then the only force acting on them is gravity, and since they were both accelerating at the same speed (one going up one going down) then no matter what their acceleration is, surely the tension in the string will be the same?

Thats what made me change my answer because before i got 39.2N but then i thought better of it and ended up with 78.4N, so if you cant recall getting either one of them, then i clearly can't do tension.

That would mean that it isnt accelerating though, as the tension equals the total mass x gravity surely? the tension would increase above (8 x 9.8) if it were accelerating?

Reply 88

nadya18

there was that question about P, mass 5kg, moves 0.196m down. Find the time it hits the ground. I think i got t=0.4 but i'm not sure

Reply 89

Hillz3

going back to the helicopter question again, i noticed in the question it said 'the helicopter set off at an acceleration of (0.5i + 0.375j). its level above sea level does not change when it is moving'
how does that relate to how you would answer the question?

Reply 90

seejay1

Original post by Hillz3

Its saying that is hovers (u=0) and it is only moving in 2 dimensions, not changing in height...

Reply 91

dannyjackson

Original post by Hillz3

It means you do not need to worry about the third dimension i.e. up or down.

Reply 92

Joshp93

Original post by nadya18

i think t=4

Well if t=4 then 78.4 is correct height, but i can only remember getting that as a tension, now im thinking i got the wrong height, but surely that would mean i would get a different value for the speed and a different angle to you guys, which i didn't i got 253ms-1 for speed and 8-9 degrees for angle, maybe i did get 78.4 as the height... i will never know :biggrin:

Reply 93

Joshp93

Original post by seejay1

That would mean that it isnt accelerating though, as the tension equals the total mass x gravity surely? the tension would increase above (8 x 9.8) if it were accelerating?

Meh, im guessing i f***ed up the tension question then... ahwell just 2 marks.

Reply 94

seejay1

Original post by Joshp93

That must have been right, as you needed the height :smile:

so I believe you got that right! If the masses of the pulley one was 8KG then you could have got 78.4 but unfortunately that would be incorrect, it was 78.4+39.2 or something, definitely over 100

Reply 95

Joshp93

Original post by seejay1

That must have been right, as you needed the height :smile:

so I believe you got that right! If the masses of the pulley one was 8KG then you could have got 78.4 but unfortunately that would be incorrect, it was 78.4+39.2 or something, definitely over 100

Just thinking, you dont need the height to work out the vertical component cos you can just use v=u+at using t=4 and a=9.8. So maybe i did get an incorrect h... ahwell, still possible for me to get an A :smile:

will take some pressure off my core 3 and core 4 exams in June, since i resat M1 being as i just did M2 in january and M1 is like 5 times easier than M2.

Reply 96

User544981

Original post by Joshp93

If i remember correctly i used s=ut+0.5at^2 to work out h, using u as 0ms-1 and a as 9.8ms-2. And i beliive they gave you a time? if anyone can remember the time it took for the projectile to hit the floor then i can work out h.

yep the time was 4 seconds i think

Reply 97

seejay1

Original post by Joshp93

will take some pressure off my core 3 and core 4 exams in June, since i resat M1 being as i just did M2 in january and M1 is like 5 times easier than M2.

I wouldnt worry its only 2 marks. How could you get the correct angle though? I think you did get the correct height :smile:

Reply 98

ezeffy

I swear in the helicopter question it sed that the helicopter had stopped accelerating?

Reply 99

Joshp93

Original post by seejay1

I wouldnt worry its only 2 marks. How could you get the correct angle though? I think you did get the correct height :smile:

The angle from which it hits the floor isnt dependent on the height or the distance it travelled i believe, instead its the two velocity components at the time it hits the floor which dictates its direction and hence the angle at which it hits the floor.