help on mechanics

Can somebody please help me on Q15 from Revision Exercise 2 in M1 (edexcel).

i've tried for sometime - but can't manage to get the answers in the back of the book.

Reply 1

Unregistered

You would get more help if you posted the question. not everyone has an 'edexcel m1' book.

Reply 2

Fermat

V3nom

Can somebody please help me on Q15 from Revision Exercise 2 in M1 (edexcel).

i've tried for sometime - but can't manage to get the answers in the back of the book.

You couldn't post the question could you - I don't have that book.

Reply 3

V3nom

two particles A and B of mass 8kg and 10kg respectively, are connected by a light inextensible string which passes over a light smooth pulley P. Particle B rests on a smooth horizontal table and particle A rests on a smooth plane inclined at 30 degrees to the horiz. with the string taut and perpendicular to the line of intersection of the table and the plane.

the system is released from rest:

a) find the magnitude of acceleration of particle B
b) find, in newtons, the tension in the in the string.
c) find the distance covered by B in the first 2 seconds of motion, given b does not reach the pulley

Reply 4

Fermat

Resolve the mass A into forces normal to the plane and pointing down the plane.

The force down the plane is,

T=Mg.cos60 , M=8kg
T=8g*0.5
T=4g N

This force is the accelerating force on the mass B.

So,
a)
T=ma, where m=10kg
or,
4g=10a
a=0.4g=3.924 m/s²

b)
T=4g=39.24 N

c)
s=ut + ½at², where u=0,t=2
s=0.5*0.4g*4
s=9.8g
s=7.85 m

Reply 5

V3nom

thanks for the help however, those aren't the answers in the back of the book. i got the same answers as you - however, the answers in the back are: a)2.18 b)21.8 c) 4.36

Reply 6

Fermat

V3nom

thanks for the help however, those aren't the answers in the back of the book. i got the same answers as you - however, the answers in the back are: a)2.18 b)21.8 c) 4.36

Hmm, those answers are all out by a factor of exactly 5/9!

Reply 7

mak101

sumtimes those edexcel books get it wrng ... :smile:

seen it quite a few times

Reply 8

Fermat

V3nom

...with the string taut and perpendicular

to the line of intersection of the table and the plane.

I don't really understand this. It isn't a typo is it?

Reply 9

V3nom

yeah - i think that might be the case. nevertheless, thanks for all your help and i'll ask my teacher if he can shed any light on it.

Reply 10

V3nom

Fermat

I don't really understand this. It isn't a typo is it?

well they have a diagram in the book - however i can't show you this

Reply 11

paladin

force down the 8kg is mgsin30
which is equal to the resultant force moving the system so
f=ma
39.2=18a
a=2.18

b_)tension = the force on the 10kg
so
f=ma
10*2.18-21.8N

c-)x=ut+.5at^2
x=0=(.5*2.18*4)=4.36

i hope that i was useful