In many practical applications, we use variable electric current I(t), that is, the current that changes with time t. A couple of examples that we will consider in this problem: (a) Current I(t)=I0 cos(2πf·t) that oscillates with frequency f. (b) Current I(t)=I0 e−t/ that decays in time with time constant . Our questions will be related to the currents with amplitude I0=1.56 A running in the copper (resistivity = 1.7 10-8 Ω·m) wire of diameter d=3 mm and length l=0.56 m. For example (a), how much energy Wa is dissipated in the wire via Joule heating during one period of current oscillations for frequency f=50.4 Hz?: Wa= mJ. With the oscillating current, the amount of charge passing through any cross-section of the wire would, of course, also oscillate with the same frequency. What is the amplitude Q0 of charge oscillations?:

Matt is driving down 7th street. he drives 150 meters in 18 sec. assuming he doesn’t slow down or speed up, what is his speed?

What is the force that opposes motion and works against the downward pull? a) friction b) gravity c) weight d) acceleration

In the future, people will only enjoy one sport: electrodisc. in this sport, you gain points when you cause metallic discs hovering on a field to exchange charge. you are an electrodisc player playing the popular four disc variant. the disks have charges of qa = −8.0 µc, qb = −2.0 µc, qc = +5.0 µc, and qd = +12.0 µc. (1) you bring two disks together and then separate them. you measure the resulting charge of these two disks and find that it is +5.0 µc per disk. which two disks did you bring together? (a) a and b (b) a and c (c)a and d (d)b and c(e) b and d (f) c and d. (2) you bring three disks together and then separate them. you measure the resulting charge of these three disks and find that it is +3.0 µc per disk. which three disks did you bring together? a, b, and c (a) a, b, and d (c) a, c, and d (d) b, c, and d. (3) given the resulting charge of each disk measured in (b) is +3.0 µc, how many electrons would you need to add to a disk of this charge to electrically neutralize it? electrons