final test; physics?

Question

1. if you have a free electron and a free proton between two oppositely charged plates, where will they go when they are released? How do the forcess on them compare? How do their accelerations compare? Which hits first?

2. The neighbors like to keep their 40.0W front porch light on at night to welcome visitors. If the light is on 6pm-7am and they pay 8.0cent per kwhr, how much does it cost to run the light for this amount of time each week?

Answer 1

The electron will move toward the positive plate, and the proton toward the negative plate. Since they have the same charge magnititude, the force on each will be the same. However, since the proton is much more massive than the electron, the electron acceleration will be much greater, and the electron will hit the plate first.

The 40W light uses 40watt-hrs in one hour. The time interval from 6pm to 7am is 13 hrs, so the total energy used is 13*40 watt hours.per day, or for one week, 7*13*40 watt hours. For kwhr, divide this by 1000, so the energy per week is 7*13*40/1000 kwhr. multiply this by $0.08 to get the total weekly cost of 7*13*40*0.08/1000 dollars per week

Answer 2

1. The proton will go towards negatively charged electrode and electron will go to the positively charged one.
Force on both will be same but F=massXacceleration and proton is very heavier than electron. So acceleration of electron will be much higher than that of proton so electron will hit the plate first if electron and proton are placed at equal distance from the plates.

2. P = kilowatt X hours
= .04 X 13 = 0.52 KW @ 8 cents/KW i.e, 4.16 cents/day.

So for a week 4.16X7 = 29.12 cents/week

Answer 3

the lamp is on 13 hours a dayfor seven days a week.so 91 hours a week.
energy consumed=power* time
40W *91 =3640 watt hours =3.64 kWh
cost per week=3.64*8=29.12c