I electromagnets, the magnetic field is turned off when there is no induced current. So, electromagnets act as magnets only when current is induced in an insulated wire wrapped around a material mage of ferromagnetic material such as iron core rotating in a magnetic field.
So, option D is the correct one.
If you wanna know more about electromagnets, write down in comments {:
The ant's resultant velocity is 0.51 m/s at 78.7°
Since the ant is moving with a velocity of 0.1 m/s in the +x direction relative to the treadmill, and the treadmill is moving 0.5 m/s in the +y direction, the magnitude of the resultant velocity of the ant relative to the ground (since both directions are perpendicular) is thus
V = √(x² + y²)
= √[(0.1 m/s)² + (0.5 m/s)²]
= √[0.01 m²/s² + 0.25 m²/s²]
= √(0.26 m²/s²)
= 0.51 m/s.
The direction is Ф = tan⁻¹(y/x)
= tan⁻¹(0.5 m/s ÷ 0.1 m/s)
= tan⁻¹(5)
= 78.69°
≅ 78.7°
The ant's resultant velocity is 0.51 m/s at 78.7°
Learn more about resultant velocity here:
brainly.com/question/15093278
Kepler's third law states that, for a planet orbiting around the Sun, the ratio between the cube of the radius of the orbit and the square of the orbital period is a constant:

(1)
where
r is the radius of the orbit
T is the period
G is the gravitational constant
M is the mass of the Sun
Let's convert the radius of the orbit (the distance between the Sun and Neptune) from AU to meters. We know that 1 AU corresponds to 150 million km, so

so the radius of the orbit is

And if we re-arrange the equation (1), we can find the orbital period of Neptune:

We can convert this value into years, to have a more meaningful number. To do that we must divide by 60 (number of seconds in 1 minute) by 60 (number of minutes in 1 hour) by 24 (number of hours in 1 day) by 365 (number of days in 1 year), and we get