How much heat is needed to raise the temperature of 9g of water by 17c?

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

A100-watt light bulb illuminates a solar cell. the electricity from the solar cell operates a water pump that delivers 1 watt of power. what is the efficiency of the system?

The center of the milky way most likely contains a. empty space. b. a red giant star. c. a globular cluster. d. a supermassive black hole.