M2 wjec 2016- Official thread

Original post by siri29

how did people do the cannon question?

Momentum, a bit mean tbh because it's not on the spec this year. for b.) the start energy is equal to the kinetic energy of the cannon and the ball added using 1/2mv^2 for both. and c.) uses the KE of the cannon and the distance travelled using work=force*distance.
hope that helps clear it up :smile:

Reply 22

Original post by SoThisIsStresful

Momentum, a bit mean tbh because it's not on the spec this year. for b.) the start energy is equal to the kinetic energy of the cannon and the ball added using 1/2mv^2 for both. and c.) uses the KE of the cannon and the distance travelled using work=force*distance.
hope that helps clear it up :smile:

And for the assumption, did you put down that all the energy from burning the charge is converted to KE for the recoiling part and the cannon ball, and none is converted to sound, heat, etc.? :holmes:

Also, at least it's from a previous mechanics module - last year they had double angle formulae in the M2 paper. :tongue:

(edited 7 years ago)

Reply 23

Original post by SoThisIsStresful

c.) uses the KE of the cannon and the distance travelled using work=force*distance.
hope that helps clear it up :smile:

I did this differently... What did you get for the magnitude of the force needed to stop the recoiling part in a distance of 1.2 m?

Reply 24

Original post by Hydeman

And for the assumption, did you put down that all the energy from burning the charge is converted to KE for the recoiling part and the cannon ball, and none is converted to sound, heat, etc.? :holmes:

Also, at least it's from a previous mechanics module - last year they had double angle formulae in the M2 paper. :tongue:

I said it was an isolated system (no other forces acting, no loss through sound, air resistance, heat etc.). yeah :smile:

Im just glad i had PH4 yesterday for that one!

Reply 25

Original post by Hydeman

I did this differently... What did you get for the magnitude of the force needed to stop the recoiling part in a distance of 1.2 m?

total KE of ONLY cannon recoiling = 0.5*1600*4.5^2 =16200J <----- this is also work needed to stop it from moving.
work=force*distance
force=16200/1.2=13500N me thinks

i have the paper here so it was easier just to re do it, hope that helps :smile:

Reply 26

Original post by SoThisIsStresful

total KE of ONLY cannon recoiling = 0.5*1600*4.5^2 =16200J <----- this is also work needed to stop it from moving.
work=force*distance
force=16200/1.2=13500N me thinks

I got double that using a different method. :sigh:

Hope C3/C4 boundaries are the same as last year; then it won't matter what result I get in M2. :tongue:

i have the paper here so it was easier just to re do it, hope that helps :smile:

Can you post a picture of it? :smile:

(edited 7 years ago)

Reply 27

SplatoonLove

I too had 1.5 for k. I remember getting 21/14 and then simplifying it to 3/2.

Reply 28

IMG_20160621_132106.jpg369.2KB

Attachment not found

Reply 29

Original post by Hydeman

I got double that using a different method. :sigh:

Hope C3/C4 boundaries are the same as last year; then it won't matter what result I get in M2. :tongue:

Can you post a picture of it? :smile:

just done

hope it worked, sorry it's bad quality :/

Reply 30

Original post by SoThisIsStresful

just done

hope it worked, sorry it's bad quality :/

Thanks.

What do you think the grade boundaries will be like? I feel like it should be similar to 2013 (considering the unusual circles question about the disc and that people who don't take physics and forgot all of M1 are likely to be thrown by the momentum question), but then I felt the same about last year's paper, and it ended up being 62/75 for an A.

(edited 7 years ago)

Reply 31

Original post by Hydeman

Thanks.

What do you think the grade boundaries will be like? I feel like it should be similar to 2013 (considering the unusual circles question about the disc and that people who don't take physics and forgot all of M1 are likely to be thrown by the momentum question), but then I felt the same about last year's paper, and it ended up being 62/75 for an A.

Honestly I have no idea, i tend not to look at grade boundaries until results day :/ i think your right though, some people i spoke to (that don't do physics) didn't even try the momentum and circles question because they had no idea. Good luck all the same :smile:

Reply 32

matthewdjones

9

Original post by Hydeman

Momentum before = momentum after for part a).
Can't remember part b) but I did do it.
Part c) was F = (m(v - u))/t, I think. You had to use time = distance/speed first though.

I thought it was Just work = force x distance

Reply 33

Original post by matthewdjones

I thought it was Just work = force x distance

I might have done that wrong. Another person (see above) did it using work = Fs and got an answer that was half of what I got.

Reply 34

Original post by SoThisIsStresful

Honestly I have no idea, i tend not to look at grade boundaries until results day :/ i think your right though, some people i spoke to (that don't do physics) didn't even try the momentum and circles question because they had no idea. Good luck all the same :smile:

Good luck to you too. :smile:

I did put some stuff down for the weird circles question, and mentioned that the units of angular velocity are radians per second, just in case there's a mark for that. :tongue:

Just hoping C3 and C4 boundaries are generous; if they are, it won't matter what I get in M2.

Reply 35

username2335163

5

Original post by SoThisIsStresful

Momentum, a bit mean tbh because it's not on the spec this year. for b.) the start energy is equal to the kinetic energy of the cannon and the ball added using 1/2mv^2 for both. and c.) uses the KE of the cannon and the distance travelled using work=force*distance.
hope that helps clear it up :smile:

i was going to do momentum but i did kinetic energy calc instead oops, but i used the same method for the rest. oh well hopefully didn't lose too many

Reply 36

username2335163

5

Original post by matthewdjones

I thought it was Just work = force x distance

i actually used suvat equations and then used f=ma

Reply 37

matthewdjones

9

Original post by siri29

i actually used suvat equations and then used f=ma

Could you assume constant acceleration?

Reply 38

username2335163

5

Original post by matthewdjones

Could you assume constant acceleration?

i took s=1.2 u= 0 (as it is at rest at the start) v=whatever you got and then calculate a and sub into f=ma

Reply 39

gkirk