Draw a p-V diagram and explain the concept of positive and negative work. Give one example each.

A gas contained in a cylinder fitted with a frictionless piston expands against a constant external pressure of $1 \mathrm{atm}$ from a volume of

$5 \mathrm{L}$ to a volume of $10 \mathrm{L}$. In doing so it absorbs $400 \mathrm{J}$ of thermal energy from its surroundings. Determine the change in internal energy of system.

A hypothetical thermodynamic cycle is shown in the figure. Calculate the work done in 25 cycles. 

The figure shows the V-T diagram for one cycle of a hypothetical heat engine which uses the ideal gas. Draw the p-V diagram and p-T diagram of the system. 

A system is taken to its final state from initial state in hypothetical paths as shown figure. Calculate the work done in each case.