A gas contained in a cylinder fitted with  a frictionless piston expands against a  constant external pressure of 1 atm from  a volume of 5 litres to a volume of 10  litres. In doing so it absorbs 400 J of  thermal energy from its surroundings.  Determine the change in internal energy  of system.
A Carnot refrigerator operates between  250K and 300K. Calculate its coefficient  of performance.
Efficiency of a Carnot cycle is 75%.  If temperature of the hot reservoir is  727ºC, calculate the temperature of the  cold reservoir.
Potential energy of a particle performing  linear S.H.M is 0.1 π² x² joule. If mass of  the particle is 20 g, find the frequency of  S.H.M.
The total energy of a body of mass 2 kg  performing S.H.M. is 40 J. Find its speed  while crossing the centre of the path.