Grinding is known to produce residual stresses on the finished surface. These residual stresses play an important role in determining the life of the component in many applications. What type of residual stresses are desirable to reduce the risk of failure due to surface cracks?

a. Compressive
b. Tensile
c. Both are disadvantageous
d. Both tensile and compressive are advantageous

An inventor claims to have developed a reversed heat engine (ie. a heat pump) which is able to deliver 10 kj heat into the room at 20°c from outside ambient temperature of -10°c by consuming only 2 kj electricity in winter. this claim is a)-impossible b)-possible only if the heat pump is ideal c)-practically possible d)-unable to be assessed as it depends on the working fluid used in the heat pump.