PHYS 10111 Lecture 9: Practice Questions

<p>An electric water heater is designed to produce 42 kW of heat when it is connected to a 240-V source. If the heater is 74 % efficient, how long would it take to heat 45 gallons of water from 20 C to 85 degrees?</p>

What impulse is needed to stop a 45 g mass traveling at a velocity of -42 m/s?

78. Silicon has three naturally occurring isotopes (Si-28, Si-29, and Si-30). The mass and natural abundance of Si-28 are 27.9769 amu and 92.2%, respectively. The mass and natural abundance of Si-29 are 28.9765 amu and 4.67%, respectively. Find the mass and natural abundance of Si-30.