1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
Kipish [7]
3 years ago
7

A reasonable estimate of the moment of inertia of an ice skater spinning with her arms at her sides can be made by modeling most

of her body as a uniform cylinder. Suppose the skater has a mass of 64 kg . One eighth of that mass is in her arms, which are 60 cm long and 20 cm from the vertical axis about which she rotates. The rest of her mass is approximately in the form of a 20-cm-radius cylinder.A) Estimate the skater's moment of inertia to two significant figures.B)If she were to hold her arms outward, rather than at her sides, would her moment of inertia increase, decrease, or remain unchanged?
Physics
1 answer:
Oxana [17]3 years ago
6 0

Answer:

A)  I_{total} = 1.44 kg m², B) moment of inertia must increase

Explanation:

The moment of inertia is defined by

     I = ∫ r² dm

For figures with symmetry it is tabulated, in the case of a cylinder the moment of inertia with respect to a vertical axis is

      I = ½ m R²

A very useful theorem is the parallel axis theorem that states that the moment of inertia with respect to another axis parallel to the center of mass is

    I = I_{cm} + m D²

Let's apply these equations to our case

The moment of inertia is a scalar quantity, so we can add the moment of inertia of the body and both arms

      I_{total}=I_{body} + 2 I_{arm}

       I_{body} = ½ M R²

The total mass is 64 kg, 1/8 corresponds to the arms and the rest to the body

       M = 7/8 m total

       M = 7/8 64

       M = 56 kg

The mass of the arms is

      m’= 1/8 m total

      m’= 1/8 64

      m’= 8 kg

As it has two arms the mass of each arm is half

     m = ½ m ’

     m = 4 kg

The arms are very thin, we will approximate them as a particle

    I_{arm} = M D²

Let's write the equation

     I_{total} = ½ M R² + 2 (m D²)

Let's calculate

    I_{total} = ½ 56 0.20² + 2 4 0.20²

    I_{total} = 1.12 + 0.32

    I_{total} = 1.44 kg m²

b) if you separate the arms from the body, the distance D increases quadratically, so the moment of inertia must increase

You might be interested in
If a sled has a mass of 4kg what is the force of gravity on the sled?
ale4655 [162]

Answer:

Explanation:

Gravity pulls everything down at the same rate of 9.8 m/s/s. If you're looking for the normal force, which is the same as the weight of the object, we'll find that, just in case.

w = mg which says that the normal force/weight of an object is equal to its mass times the pull of gravity:

w = 4.0(9.8) so

w = 39N

7 0
3 years ago
A boat leaves the dock at t = 0.00 s and, starting from rest, maintains a constant acceleration of (0.461 m/s2)i relative to the
liberstina [14]

Answer:

At t=4.82 s, the boat is moving at 3.464 m/s.

At t=4.82 s, the boat is 13.112 m from the dock.

Explanation:

The speed of the boat in j'th direction remains constant for all times (vj=2.16 m/s), however, the speed in i'th direction is changing due to the constant acceleration (0.461 m/s^2)i.

In order to find the velocity of the boat a t=4.82 s, first we need to compute the velocity of the boat relative to the water in the i direction (vi_b) at t=4.82 s:

vi_b = a*t = (0.461 m/s^2)*(4.82 s) = 2.222 m/s

Now, we add this velocity to the velocity of the water in the i direction:

vi = vi_b + vi_w = 2.222 m/s + 0.486 m/s = 2.708 m/s

Therefore, the speed of the boat at t = 4.82 s is: v = (vi, vj) = (2.708, 2.16) m/s. Finally, to find its speed, we just calculate the magnitude of v and obtain that the speed is: 3.464 m/s.

For the second question, first we will find the distance that the boat moved in the i'th direction and then in the j'th direction.

The speed in the i'th direction, for all times, is given by:

(0.485 + 0.461*t) and in order to find the distance advanced in the i'th direction (di) during 4.82 s, we need to integrate this velocity:

di = 0.485*t + (0.461*t^2)/2 (evaluated from t=0 to t =4.82) = 0.485*(4.82) + (0.461*(4.82)^2)/2 = 2.337 + 5.634 = 7.971 m

The speed in j'th direction, for all times, is given by:

2.16 and in order to find the distance advanced in the j'th direction (dj) during 4.82 s, we need to integrate this velocity:

dj = 2.16*t (evaluated from t=0 to t =4.82) = (2.16)*(4.82) = 10.411 m

Using Pythagoras' Theorem, we find that the the boat is at 13.112 m from the dock at t = 4.82 s.

4 0
3 years ago
The spectra of most galaxies show redshifts. this means that their spectral lines _________.
spin [16.1K]
Have wavelengths that are longer than normal.
3 0
3 years ago
Difference between sold and liquid​
Tcecarenko [31]

Explanation:

Solids have closely packed particles and vibrate about a fixed position, they also have a fixed volume.

liquid have close particles but which are able to move with a bit of kinetic energy, for this reason they have no fixed volume but take the volume of the container or vessel

4 0
2 years ago
(PLEASE HELP) What area of the Earth's mantle is the densest?
Nady [450]
The area nearest to the earth's core is the densest.. 
So your answer would be letter choice ( D ) . . . 

Hope it Helped :) 
7 0
3 years ago
Read 2 more answers
Other questions:
  • Physics question, please show work for brainliest :)
    15·2 answers
  • Choose all of the true statements regarding the relationship between voltage, resistance, and current.
    15·2 answers
  • What do you know about stars?
    8·2 answers
  • How do i calculate acceleration? pls help! thanks :)
    15·1 answer
  • A single, nonconstant force acts in the + x ‑direction on an object of mass M that is constrained to move along the x ‑axis. As
    13·1 answer
  • The current in the circuit shown is 2.0 A.
    15·2 answers
  • 1.) A ball is thrown horizontally from the top of a building. What is the vertical velocity of the ball after 1 second?
    14·2 answers
  • A spring stretches from 10cm to 22cm when a force of 4n is applied, if it obeys Hooke’s law,its total length in cm when a force
    9·1 answer
  • PLEASEEEEE HELP ME !!!
    9·1 answer
  • If 14:15=42:x find the value of x​
    7·2 answers
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!