H&N Chapter 11
a. Both statements are true.
b. Both statements are false.
c. The first statement is true; the second statement is false.
d. The first statement is false; the second statement is true.
A circuit contains six 60-W lamps with a resistance of 240−Ω each and a 10.0−Ω heater connected in parallel. The voltage across the circuit is 120 V. Find the current in the circuit for the following situations. a. Four lamps are turned on. b. All of the lamps are turned on. c. Six lamps and the heater are operating.
An object with cross section A is shot horizontally across frictionless ice. Its initial velocity is v0x at t0=0 s. Air resistance is not negligible. a. Show that the velocity at time t is given by the expression
b. A 1.6-m-wide, 1.4-m-high, 1500 kg car with a drag coefficient of 0.35 hits a very slick patch of ice while going 20 m/s. If friction is neglected, how long will it take until the car's speed drops to 10 m/s ? To 5 m/s ?
Determining the Charge on U and L Tapes. Prepare a U tape and an L tape, and hang them from your desk. Test them with your hand to make sure they are both charged. Rub a plastic pen or comb on your hair (clear plastic seems to charge best), or on a piece of cotton or wool, and bring it close to each tape. You should observe that one of the tapes is repelled by the pen, and one is attracted to it. Knowing that the plastic is negatively charged, what can you conclude about the sign of the electric charge on U tapes? On L tapes? These results may be reversed if you try a different brand of "invisible tape." Be sure to compare your results with those of other students. Make sure you all agree on the assignment of "+" and "-" labels to your tapes. (If other groups are using different brands of tape, you may disagree on whether U tapes or L tapes are positive, but the electric interactions between your + tapes and their + tapes should be repulsive!) In any of your experiments, did you find any objects, other than tapes or a charged comb or pen, that repelled a U or L tape? If so, those objects must have been charged. List these objects and whether the charge was + or -.