A 20.0-kg package is dropped from a high tower in still air and is "tracked" by a radar system. When the package is 25 m above t
1 answer:
Answer:
56 N
Explanation:
There are only two forces acting on the package:
- The force of gravity, directed downward, equal to
where m is the mass of the package and g is the acceleration due to gravity
- The air resistance, acting upward, let's label it with
According to Newton's second law, the resultant of the two forces must be equal to the product between the mass, m, and the acceleration, a:
where we have:
m = 20.0 kg
g = 9.8 m/s^2
a = 7.0 m/s^2 is the acceleration when the package is at 25 m above the ground.
Substituting into the equation, we can find the magnitude of the air resistance at that altitude:
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Answer and Explanation:
This experiment is known as Lenz's tube.
The Lenz tube is an experiment that shows how you can brake a magnetic dipole that goes down a tube that conducts electric current. The magnet, when falling, along with its magnetic field, will generate variations in the magnetic field flux within the tube. These variations create an emf induced according to Faraday's Law:
This emf induced on the surface of the tube generates a current within it according to Ohm's Law:
This emf and current oppose the flux change, therefore a field will be produced in such a direction that the magnet is repelled from below and is attracted from above. The magnitude of the flux at the bottom of the magnet increases from the point of view of the tube, and at the top it decreases. Therefore, two "magnets" are generated under and above the dipole, which repel it below and attract above. Finally, the dipole feels a force in the opposite direction to the direction of fall, therefore it falls with less speed.
