Understanding Electrical Circuits and Power: Questions 10&11

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
1 reply · 2K views
C0balt
Messages
7
Reaction score
0

Homework Statement


Questions 10&11 in pictures.

Homework Equations


P=IV
W=VIt
W=Pt

The Attempt at a Solution


For 10a) P=IV
P=70*14= 980W.
10b) P=IV
1500=12*I
I=125A (which is massive so probably wrong)
10c)P=IV
60=I*12
I=5A
The 8A fuse because the current flowing through each headlamp should be 5A. Anymore than that could be dangerous.
10d) W=VIt
W=12*1*62
W=744J (which is quite low??)
10e)
W=Pt
It just doesn't give me the right answer as the sidelights appear to use more than the whole battery capacity if left on for 12 hours, which makes me believe I've done the whole of Q10 wrong.
Q11)
Maybe you could work out the work done / GPE then you could use P=W/t to work out how much power the car needs to go up the hill? (Using an hour as t from the 90km/h?)

I would greatly appreciate any help.
 

Attachments

  • image.jpg
    image.jpg
    30.8 KB · Views: 442
  • image.jpg
    image.jpg
    34.2 KB · Views: 457
  • image.jpg
    image.jpg
    39.1 KB · Views: 470
Physics news on Phys.org
C0balt said:

Homework Statement


Questions 10&11 in pictures.

Homework Equations


P=IV
W=VIt
W=Pt

The Attempt at a Solution


For 10a) P=IV
P=70*14= 980W.
10b) P=IV
1500=12*I
I=125A (which is massive so probably wrong)
10c)P=IV
60=I*12
I=5A
The 8A fuse because the current flowing through each headlamp should be 5A. Anymore than that could be dangerous.
10d) W=VIt
W=12*1*62
W=744J (which is quite low??)
10e)
W=Pt
It just doesn't give me the right answer as the sidelights appear to use more than the whole battery capacity if left on for 12 hours, which makes me believe I've done the whole of Q10 wrong.
Q11)
Maybe you could work out the work done / GPE then you could use P=W/t to work out how much power the car needs to go up the hill? (Using an hour as t from the 90km/h?)

I would greatly appreciate any help.

Your answer for 10b) is correct. Starter motors take a large amount of current to turn the engine over. They do so for only a short time, however, lest the battery be drained completely.