A bar of iron with mass 45 kg is cooled from 50℃ to 20℃. How much thermal energy does the bar of iron lose? The specific heat of iron is 470 kg/kg*C.

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.

What are the dimensions of the cross section that passes through the points a, f, g, and d?

Describe how the motion of a spring being pushed forward and backward is similar to the motion of air particles in a sound wave.