Turn on thread page Beta
 You are Here: Home >< Physics

# Escape velocity question watch

Announcements
1. I have forgotten how to work out the escape velocity of a gravitational field once the gravitational potential of the surface has been worked out, help would be appreciated.

Here is the question;

The asteroid Cere's has a mass of 7.0x10^20 Kg and a radius of 550Km

a) What is the gravitational potential at the surface of Cere's?

Which I can do and the answer came out as -8.50x10^4 JKg^-1

b) What is the min escape velocity from the surface?

Need help here
2. The PE of the object at infinity (where it can be said to have escaped from the gravitational field of the mass) is zero.
If you know the PE on the surface (a negative value), then you would need to give it that amount of energy to get it to infinity.
If this energy is initially kinetic, then just equate the initial ½mv² of the object to this PE value.
v in this case would be the speed needed to escape.
3. (Original post by Stonebridge)
The PE of the object at infinity (where it can be said to have escaped from the gravitational field of the mass) is zero.
If you know the PE on the surface (a negative value), then you would need to give it that amount of energy to get it to infinity.
If this energy is initially kinetic, then just equate the initial ½mv² of the object to this PE value.
v in this case would be the speed needed to escape.
But I don't know the mass of the escaping object, the question just asks for the minimum escape velocity so I thought I wouldn't be able to use 1/2mv^2

I don't understand how to work out the escape velocity without the mass.
4. (Original post by TheJ0ker)
But I don't know the mass so I thought I wouldn't be able to use 1/2mv^2

I don't understand how to work out the escape velocity without the mass.
It cancels.
5. (Original post by Stonebridge)
It cancels.
Ah I see now, cheers for your help.

Turn on thread page Beta
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:
Updated: September 25, 2011
Today on TSR

And I hate it

### University open days

• Manchester Metropolitan University
Wed, 14 Nov '18
• University of Chester
Wed, 14 Nov '18
• Anglia Ruskin University
Ambitious, driven, developing your career & employability? Aspiring in your field, up-skilling after a career break? Then our Postgrad Open Evening is for you. Postgraduate
Wed, 14 Nov '18
Poll

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