The initial volume of the gas is (keeping in mind that [tex]1.0 L= 1 \cdot 10^{-3} m^3[/tex]):
[tex]V_i = 2.90 L= 2.90 \cdot 10^{-3}m^3[/tex]
The work done by the external force on the gas is
[tex]W= -p \Delta V=-p (V_f - V_i)= -pV_f + pV_i[/tex]
where p is the pressure and [tex]V_f [/tex] the final volume. Re-arranging this equation, we can find the final volume Vf:
[tex]V_f = V_i - \frac{W}{p}=2.90 \cdot 10^{-3} m^3 - \frac{170 J}{7.1 \cdot 10^4 Pa} =0.5 \cdot 10^{-3} m^3 = 0.5 L [/tex]
and this value makes sense, because it is less than the initial volume of the gas, in fact the problem says that the external force compresses the gas.
