You are Here: Home >< Physics

# OCR G484 Jan 2011?

Announcements Posted on
Four hours left to win £100 of Amazon vouchers!! Don't miss out! Take our short survey to enter 24-10-2016
1. For 1bii of the Spring 2011 Newtonian World paper we are asked to calculate the momentum of descending air, force provided by the blades, and the mass of a helicopter.

In the previous part I calculated the mass of air to be 6126kg, which was correct. Given that the velocity is 12ms-1, I made the momentum to be 7.4x10^4, again correct.

But on the next part when we're asked to calculated the force provided by the helicopter blades, the mark scheme has done: mv/r.

Surely it should be mv^2/r?

That's the equation provided by the data booklet, and it makes sense, so why are they only using mv not mv^2? Or is it an error?

Thanks again!

Posted from TSR Mobile
2. (Original post by Scitty)
For 1bii of the Spring 2011 Newtonian World paper we are asked to calculate the momentum of descending air, force provided by the blades, and the mass of a helicopter.

In the previous part I calculated the mass of air to be 6126kg, which was correct. Given that the velocity is 12ms-1, I made the momentum to be 7.4x10^4, again correct.

But on the next part when we're asked to calculated the force provided by the helicopter blades, the mark scheme has done: mv/r.

Surely it should be mv^2/r?

That's the equation provided by the data booklet, and it makes sense, so why are they only using mv not mv^2? Or is it an error?

Thanks again!

Posted from TSR Mobile
They've actually used .
is the formula for centripetal force - the force towards the centre of a circle required to maintain the circular motion.

The fact that the helicopter blades are rotating is irrelevant to the question.
3. Force is equal to momentum over time

F = mv/t
4. Ah okay! Thank you! That makes sense now

Posted from TSR Mobile

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 2, 2016
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

### Who is getting a uni offer this half term?

Find out which unis are hot off the mark here

### How to get a 1st class degree

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.