A spinning ice skater on extremely smooth ice is able to control the rate at which she rotates by pulling in her arms. Which of
1 answer:
Answer:
Correct -> Her angular momentum remains constant.
Explanation:
If the skater pulls her arms, her radius changes, so her moment of inertia changes.
By definition, moment of inertia is the resistance to rotation. So, if her moment of inertia decreases, her angular velocity increases, because if there is no external torque (in this question there is none), angular momentum is conserved.
If the moment of inertia decreases by half, the angular velocity doubles. In that case kinetic energy also increases, because the square of the angular velocity affects the kinetic energy more than the decrease of the moment of inertia.
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Answer:
a) 1.68 N b) 0 c) 14.5º
Explanation:
a)
- The force on a charge moving in a magnetic field, is a vector perpendicular to the plane defined by the velocity of the charge and the magnetic field.
- The magnitude of the force F is given by the following expression:
- where q= magnitude of the charge of the particle, v=velocity of the particle, B= magnitude of the magnetic field, and θ= angle between v and B.
- Replacing by the known values in (1) we have:
- The maximum possible value of F happens when sin θ =1
- This means that v and B are perpendicular each other (in the same plane)
- So, Fmax = 1.68 N
b)
- If the maximum possible value of F happens when sin θ = 1, the minimum possible is when sin θ = 0.
- In this case, when v and B are parallel each other, the force is just 0.
c)
- If the force is 0.25 of the maximum possible, (which is when sin θ =1), this means that sin θ = 0.25, as it can be seen below:
- The angle between the velocity v and the magnetic field B is 14.5º.