3,5,7 and 9

3. A freight elevator is built to lift a long ton (2200 lbs) a distance of 100 feet in 30 seconds. It is driven by an AC motor. The energy efficiency of the gears and cables) is 85%. What is the required power output of the motor? 4. What is the torque (in Nm ) on a turbine shaft that transmits 15MW at (a) 1800rpm and (b) 3600rpm ? 5. A synchronous electric motor consumes 25.1 kilowatts of electrical power and delivers 30.7hp at 1800rpm. What is its efficiency? 6. An AC induction motor provides 21hp with an efficiency of 89.2% at 3550rpm. How much electrical power does it require (in kW )? 7. An Olympic weightlifter performing a lift called the snatch must raise a barbell in one uninterrupted motion from the floor to a position overhead. In 1988, the Russian lifter Alexandre Kourlovitch set a record by lifting 212 kg in the snatch. (a) How much work did Kourlovitch do on the weight? (b) What was his average power output? (c) What was the change in the potential energy of the weight? Be sure to list any assumptions you make. 8. Meteor Crater, near Flagstaff, Arizona, is an impact crater that measures 1200m from rim to rim and 200m from rim to floor. Geologists have estimated that the meteor itself was about 30m in diameter, and that it struck the earth at a speed of 15km/s (Skinner and Porter, 1992). Meteorite fragments collected near the crater are 92% iron and 7.1% nickel. (a) Calculate the kinetic energy of the meteor before impact. (b) Calculate the energy of the resulting explosion in tons of TNT. 9. The earth rotates on its axis once in 23.93 hours. The earth completes one revolution of the sun in 365.2425 days. (a) Compute the translational kinetic energy of the earth. (b) Compute the rotational kinetic energy of the earth