According to the law of conservation of energy. a. an object loses most of its energy as friction. b. the total amount of energy for a system stays the same. c. the potential energy of an object is always greater than its kinetic energy. d. the kinetic energy of an object is always greater than its potential energy.

Consider a 1000 w iron whose base plate is made of 0.5 cm thick aluminum alloy 2024-t6 (ρ = 2770 kg/m3 and cp = 875 j/kg°c). the base plate has a surface area of 0.03 m2. initially, the iron is in thermal equilibrium with the ambient air at 22°c. assuming 90% of the heat generated in the resistance wires is transferred to the plate, determine the minimum time needed for the plate temperature to reach 200°c.