# How this unit comes like that ?

1. Nov 3, 2012

### manal950

How this unit comes

R = specific volume X (pressure / Temperature )

0.9m^3/kg (1.3X10^5 N/m^2 / 408 K )

R = 286 KJ/KgK

please can any one explain to me how the unit ( KJ/KgK ) comes ??

2. Nov 3, 2012

### Staff: Mentor

kJ/(kg*K) - looks quite straightforward, where is the problem?

3. Nov 3, 2012

### manal950

Hi sir .. I know the unit is correct but when I try to solve by my self I don't get that uint

4. Nov 3, 2012

### AJ Bentley

r = volume * pressure / temperature
= (length*length*length)/mass * Newtons/(length*length) / temperature
= length*Newtons/(temperature * mass)

= Joules/(temperature * mass)

5. Nov 3, 2012

### Staff: Mentor

Show what you did then and we will try to find out where did you get wrong.

6. Nov 3, 2012

### Staff: Mentor

1 Joule = 1 N-m

7. Nov 4, 2012

### Staff: Mentor

Dash that looks like a minus is not the luckiest selection of the symbol in this context.

1 Joule = 1 Newton * m

is much less ambiguous.