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Official BMAT question!

The diagram shows a simplified version of the brake pedal of a car.

A driver applies a force of 30N to the pedal. What force is applied to the piston?

Now i wish i had done AS physics :rolleyes:

brake pedal.JPG14.1KB

OP

anyone?

is that Q from the short specimen paper downloaded from the bmat website?
just because my printout of the paper shows 60N applied to the pedal.

But if you were to use the 30N applied force;

moment = force x perpendicular distance to pivot

moment exerted by 30N force on pedal = 30N x (16cm + 4cm)
= 600 Ncm

force applied to piston = 600 Ncm / 4cm
= 150N

Reply 3

Yeti-Boy

F1 * r1 = M1 F2 * r2 = M2 According to the lever law M2 + M1 = 0 so M2 = M1
F1 = 30 r1 = .2 F2 = answer r2 = .04 So (30 * .2)/ .04 = F2 = 150

Reply 4

Library

OP

2

Yellowmellow

is that Q from the short specimen paper downloaded from the bmat website?
just because my printout of the paper shows 60N applied to the pedal.

But if you were to use the 30N applied force;

moment = force x perpendicular distance to pivot

moment exerted by 30N force on pedal = 30N x (16cm + 4cm)
= 600 Ncm

force applied to piston = 600 Ncm / 4cm
= 150N

why do you divide by 4?

Reply 5

Yeti-Boy

Moment 1 = Moment 2 So when moment one is 600 Ncm Moment 2 is 600Ncm
Moment 2 = 4cm * Force So the Force is 600/4= 150 N

Reply 6

Jakyboi

Moment = force x perpendicular distance from pivot

Clockwise moment = anticlockwise moment
30 x (16+4) = 4 x F
600 = 4F
F = 600/4
= 150N

You got it?

Reply 7

Ribbons

12

Elektrafy

Moment = force x perpendicular distance from pivot

Clockwise moment = anticlockwise moment
30 x (16+4) = 4 x F
600 = 4F
F = 600/4
= 150N

You got it?

but if you're taking moments about the pivot, dont BOTH the forces cause anticlockwise moments?

Reply 8

Flipper05

Ok....why do these BMAT questions seem harder then the ones in the GCSE revision guides!!!!

It's been far too long since i did Physics...

Reply 9

Elles

17

because it's GCSE level knowledge/facts - not application.

come on, you all probably got As/A*s in GCSE science :wink:

- the BMAT has to do a little more than just duplicate GCSE questions when trying to discriminate between top A level students! :p:

Reply 10

Chewwy

17

PSdilemma

but if you're taking moments about the pivot, dont BOTH the forces cause anticlockwise moments?

yes they do.

clockwise moments = anticlockwise moments iff no resultant force. but in this case there clearly is.

Reply 11

Ribbons

12

chewwy

yes they do.

clockwise moments = anticlockwise moments iff no resultant force. but in this case there clearly is.

and doesnt that mean doing the question that way is wrong?

Reply 12

pkchips

1

Library

why do you divide by 4?

Because moments = force x perpendicular distance

In this case, perpendicular distance is 4 and moments is 600

So force = 600/4

And also, the forces aren't both acting in one direction. The brake pedal is going in one direction, and the piston is exerting a force in the opposite direction as you need to overcome the "resistance" of the piston to moving, and the piston is exerting an equal and opposite force on the pedal.

Reply 13

your.angel

1

Elles

because it's GCSE level knowledge/facts - not application.

come on, you all probably got As/A*s in GCSE science :wink:

- the BMAT has to do a little more than just duplicate GCSE questions when trying to discriminate between top A level students! :p:

That's ok so long as you've just done your GCSEs...I've just discovered how much you can forget in 5 years... *cries* I'm just looking forward to the essay - that at least is one thing uni prepares you for!

Reply 14

Marie05

1

i thought that the distance should be converted from cm to metres !
--------------
which gives the same answer anyways :p:

!!

Official BMAT question!

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