## Question 2004 Q1a

### Floorball Maniac

Posted 12 May 2006 - 07:58 AM

I am probably missing something obvious here but I do not get this question.

Calculate the speed at which the reletavistic mass of an object is equal to three times its rest mass.

There is no other information in the question. It is worth 2 marks. Can anyone help me here?

Thank you!

### colinH

Posted 12 May 2006 - 10:57 AM

since the relativistic mass is equal to 3 times the rest mass, you can replace m in the equation for 3mo
i.e

3 mo = ( mo / (1- (v^2 / c^2))^1/2

then rearrange to get:

3 mo * (1 - (v^2/c^2))^1/2 = mo

so divide through by 3 mo to get

(1 - (v^2 / c^2))^1/2 = 0.333 (a third)

so (1 - (v^2 / c^2)) = 0.111 (square both sides)

so (v^2 / c^2) = 0.888

so (V^2) = 0.888 * c^2

= 8*10^16

therefore v = 2.83*10^8 ms-1

sorry I don't know how to show square root signs and things so it is a bit confusing but I hope this helps!

### Floorball Maniac

Posted 12 May 2006 - 11:26 AM

Superb help! Thank you very much!

### Jason Bourne

Posted 12 May 2006 - 10:08 PM