a) Firstly, find the energy used.
By E=PT,
energy used = 1200W x (2 x60)s
= 144000J
Then, find the specific heat capacity.
By c = E/m△T,
c = 144000J/2kg x (60°-28°)
= 2250J kg^-1 °C^-1
b)The reality specific heat capacity of oil is larger than the calculated one. It is because the some energy from the heater lost to the surroundings . therefore, in reality more energy is needed to rise the 1kg of oil 1°C.