An elevator has an electrical power rating of 3.2 x 104 W.  If the elevator takes 42 s to move up 3 floors (12 m total), what is its efficiency?  Assume the mass of the elevator and its passengers is 1800 kg.

a) Assume that people can go to work from home either by SkyTrain or by car. Driving takes 10 min if there is no one else using the road, while SkyTrain always takes 20 min. If there are N other cars using the road, it takes C=N/50+10 min for each person to drive. Suppose we ignore the energy cost and only focus on the time cost. What is the efficient number of cars on the road? Assume SkyTrain always has enough space and you pay $3 for each ride, and the time cost is 1$/min for each traveler. Also assume that the operation cost of Skytrain is independent of the number of passengers.

7. A crate of mass 10.0 kg is pulled up a rough incline with an initial speed of 1.50 m/s. The pulling force is 100 N parallel to the incline, which makes an angle of 20.0° T with the horizontal. The coefficient of kinetic friction is 0.400, and the crate is pulled 5.00 m. (a) How much work is done by the gravitational force on the crate? (b) Determine the increase in internal energy of the crate- incline system owing to friction. (c) How much work is done by the 100-N force on the crate? (d) What is the change in kinetic energy of the crate? (e) What is the speed of the crate after being pulled 5.00 m?

As an object moves from point A to point B only two forces act on it: one force is nonconservative and does -40 J of work, the other force is conservative and does -60 J of work. Between A and B, O A. the potential energy of object increases, mechanical energy increases O B. the potential energy of object decreases, mechanical eneray increases O C. the potential energy of object decreases, mechanical eñey decreases the potential energy of object increases, mechanical energy decreases