Answer:
v = 18.84 m/s
Explanation:
Given that,
The length of the string, r = 1.5 m (it will act as radius)
The rubber stopper makes 120 complete circles every minute.
Since, 1 minute = 60 seconds
It means, its frequency is 2 circles every second.
Let we need to find the average speed of the rubber stopper. It can be calculated as follows :

d is distance,
and 1/T = f (frequency)

So, the average speed of the rubber stopper is 18.84 m/s.
The answer for the following problem is explained below.
Therefore the volume charge density of a substance (ρ) is 0.04 ×
C.
Explanation:
Given:
radius (r) =2.1 cm = 2.1 ×
m
height (h) =8.8 cm = 8.8 ×
m
total charge (q) =6.1×
C
To solve:
volume charge density (ρ)
We know;
<u> ρ =q ÷ v</u>
volume of cylinder = π ×r × r × h
volume of cylinder =3.14 × 2.1 × 2.1 ×
× 8.8 ×
volume of cylinder (v) = 122.23 ×
<u> ρ =q ÷ v</u>
ρ = 6.1×
÷ 122.23 ×
<u>ρ = 0.04 × </u>
<u> C</u>
Therefore the volume charge density of a substance (ρ) is 0.04 ×
C.
I think the correct answer from the choices listed above is option B. The very high voltage needed to create a spark across the spark plug is produced at the transformer's secondary winding. <span>The secondary coil is engulfed by a powerful and changing magnetic field. This field induces a current in the coils -- a very high-voltage current.</span>
If "0.3 minute" is correct, then it's 9,543,272 Joules.
If it's supposed to say "0.3 SECOND", then the KE is 2,651 Joules.
Energy is calculated as power*time, so give the wattage of 1200 W (equivalent to 1200 Joules/second) and time of 30 seconds, multiplying these gives 36000 J or 36 kJ of electrical energy.
If electrical charge or current is needed: Power = voltage * current, so given the power of 1200 watts and voltage of 120 V, current is 1200 W / 120 V = 10 Amperes. Charge is calculated by multiplying 10 A*30 s = 300 C.