Answer:
frequency = 1475.45 Hz
Explanation:
given data
frequency f1 = 1215 Hz,
frequency f2 = 1265 Hz
police car moving vp = 25.0 m/s
solution
speed of sound u = 343 m / s
speed of the other car = v
when the police car is stationary
the frequency the other car receives is
f2 = f1 ×
................1
and
the frequency the police car receives is
f2 = f1 ×
..................2
now from equation 1 and 2


v = 4.77 m/s
and
frequency the other car receives is
f2 = f1 ×
......................3
and
the frequency the police car receives is
f2 = f1 ×
.......................4
now we get
f2 = f1 ×
f2 =
f2 = 1475.45 Hz
Work done = force x distance = 40 x 2 = 80 Joules.
The electric current passing through the bulb would be 3.3A
<u>Explanation:</u>
Given:
Electric charge, q = 800C
Time, t = 4 min
= 4 X 60 sec
= 240 sec
Electric current, I = ?
We know,

On substituting the value we get:

Thus, the electric current passing through the bulb would be 3.3A
Answer:
Current, I = 1000 A
Explanation:
It is given that,
Length of the copper wire, l = 7300 m
Resistance of copper line, R = 10 ohms
Magnetic field, B = 0.1 T

Resistivity, 
We need to find the current flowing the copper wire. Firstly, we need to find the radius of he power line using physical dimensions as :




r = 0.00199 m
or

The magnetic field on a current carrying wire is given by :



I = 1000 A
So, the current of 1000 A is flowing through the copper wire. Hence, this is the required solution.