A rock weighs 30 N in air and 25 N when completely submerged in a fluid with a density of 750 kg/m3.   Determine the density of the rock.

In a well-insulated container, 4.0 kg of water and 3.0 kg of ice are in thermal equilibrium at 0 °C. How much heat is required to bring the system to thermal equilibrium at 45 °C?

What is the pressure difference between the street level and the roof of a 400 m high tower?  (Assume the density of air is 1.29 kg/m3 )

Water enters a pipe of diameter 5 cm with a velocity of 4 m/s. Then the water encounters a constriction and its velocity becomes 16 m/s. What is the diameter of the constricted portion of the pipe?

A system containing an ideal gas at a constant pressure of 1.32 × 105 Pa gains 2120 J of heat.  During the process, the internal energy of the system increases by 2640 J.  What is the change in volume of the gas?

A circular hole in a copper plate is 3.925 cm in diameter at 30.0 °C.  What is the diameter of the hole if the temperature of the plate is raised to 150.0 °C?  The coefficient of linear expansion of copper is 17 × 10–6/C°. 

Sphere 1 has an emissivity of 0.8, its radius is 1 m, and its temperature is 25 °C. Sphere 2 has an emissivity of 0.4, and a radius of 1 m. What should be the temperature of Sphere 2 so it emits radiation at the same power as Sphere 1?   

A heat engine is used to lift a 4500-kg load to a height of 3 m at a constant speed. During the lifting process, the engine received 400,000 J of heat from the fuel burned in its interior. What is the efficiency of the engine?

Sphere 1 has an emissivity of 0.85, its radius is 1 m, and its temperature is 35 °C. Sphere 2 has an emissivity of 0.45 and a radius of 1 m. What should be the temperature of Sphere 2 so it emits radiation at the same power as Sphere 1? 

A student does 1290 J of work while studying.  In the process, her internal energy decreases by 2490 J.  Determine the value of Q, including the algebraic sign.