Circular Motion, Work, and Power Bonus Problems

1.) A 193 kg curtain needs to be raised 7.5 m in as close to 5 s as possible. Three motors are available. The power ratings for the three motors are listed as 1 kW, 3.5 kW, and 5.5 kW. Prove which motor is best for the job.

2.) A flight attendant pulls her 70 N flight bag a distance of 253 m along a level airport floor at a constant speed. The force she exerts is 40 N at an angle of 52 degrees above the horizontal. Find the following: a.) the work she does on the flight bag b.) the work done by the force of friction on the flight bag c.) The coefficient of kinetic friction between the flight bag and the floor.

3.) A pilot performs an evasive maneuver by diving vertically at 320 m/s. If he can withstand an acceleration of 9.0g’s without blacking out, at what altitude must he begin to pull out of the dive to avoid crashing into the sea?

4.) Tarzan (m=85kg) tries to cross a river by swinging from a 10.0 m long vine. His speed at the bottom of the swing, just as he clears the water, is 8.0 m/s. Tarzan doesn’t know that the vine has a breaking strength of 1.0*103 N. Prove whether he makes it safely across the river.

5.) An air puck of mass .025 kg is tied to a string and allowed to revolve in a circle of radius 1.0m on a frictionless horizontal surface. The other end of the string passes though a hole in the center of the surface and a mass of 1.0 kg is tied to it. The suspended mass remains in equilibrium while the puck revolves on the surface. (a) What is the magnitude of the force that maintains circular motion acting on the puck? (b) What is the linear speed of the puck?

6.) Calculate the power required to propel a 1000 kg car at a constant velocity of 20 m/s up a straight slope inclined 5 degrees above the horizontal. Neglect friction and air resistance.

7.) How much work is required to stop an electron (m=9.11*10-31) which is moving with a speed of 1.9*106 m/s?

8.) How much work must be done to stop a 1000 kg car traveling at 110 km/h?

9.) An automobile is traveling along a highway at 90 km/h. If it travels instead at 100 km/h, what is the percent increase in the kinetic energy of the automobile?

10.) How long will it take a 1750 W motor to lift a 285 kg piano to a sixth story window 16 m above? 11.) If a car generates 18 hp when traveling at a steady 90 km/h , what must the average force exerted on the car due to friction and air resistance?

12.) How much work can a 3 hp motor do in 1 hour?

13.) A shot putter accelerates a 7.3 kg shot from rest to 14 m/s. If this motion takes 2 s, what average power was developed?

14.) A pump is to lift 8 kg of water per minute through a height of 3.5 m. What output rating should the pump motor have?