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andreyandreev [35.5K]
3 years ago
13

Una mujer de masa m está parada en el borde de una mesa giratoria horizontal de momento de inercia I y radio R. La mesa al princ

ipio está en reposo y tiene libertad de moverse alrededor de un eje vertical sin fricción que pasa por su centro. La mujer empieza a caminar alrededor de la orilla en direción de las manecillas del reloj (vista desde arriba) a una velocidad constante v en relación a la Tierra.
a) En qué dirección y con qué velocidad angular gira la mesa?

b) Cuál es el trabajo efectuado por la mujer para poner en movimiento la mesa?
Physics
1 answer:
Dovator [93]3 years ago
3 0

r

- \frac{mR^2 }{I  } \ vAnswer:

a)      w = - \frac{m r }{I} v  ,  b)   W = - ½ m_woman R² (1 + m_woman R / I²) v²

Explanation:

a) To solve this exercise, let's use the conservation of angular momentum.

We define a system formed by the table and the woman, therefore the torques are internal and the moment is conserved

initial instant. Before starting to move the woman

         L₀ = 0

final instant. After starting to move

         L_f = I w + m v r

the moment is preserved

        L₀ = L_f

         0 = Iw + m v r

         w = - \frac{m r }{I} v                    (1)

the direction of the angular velocity is opposite to the direction of the linear velocity, that is, counterclockwise

b) for this part we use the relationship between work and kinetic energy

        W = ΔK

in this case the initial speed is zero and the final speed of the table, using the relationship between linear and angular variables

         v = w r

we substitute

          W = 0 - ½ I_total w²

          I_total = I + m_{woman} R²

          W = - ½ (I + m_woman R²)  ( \frac{m_{woman} R}{I} \ v) ²

          W = - ½ (m_woman² R² + m_woman³ R³ / I²) v²

          W = - ½ m_woman R² (1 + m_woman R / I²) v²

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a bike is moving with a velocity of 90km/hr.after applying break it stops in 5 sec. calculate the force applied by brakes .mass
pentagon [3]

Explanation:

initial velocity(u) = 90 km/s = 25 m/s

time (t) = 5 sec

mass (m) = 200 kg 

final velocity (v) = 0 m/s

v = u + at 

0 = 25 + a * 5

-25 = 5 a

-5 = a

Therefore acceleration = -5m/s²

Force = mass * acceleration 

F = 200*-5

F = -1000 N

7 0
3 years ago
A very long train is rolling at 4 m/s along a straight track. An observer is standing on the ground very dangerously close to th
hichkok12 [17]

Answer:

A. \vec{r}=(6\frac{m}{s})t\ \ \hat{i}

B.  t = 50 s

Explanation:

A. The vectorial equation of the person who is getting closer to the other person is:

\vec{r}=\vec{v}t

r: position vector

v: speed vector = 6m/s i  (if you consider the motion as a horizontal motion)

Then, you replace and obtain:

\vec{r}=(6\frac{m}{s})t\ \ \hat{i}

B. The time is:

t=\frac{d}{v}

d: distance to the observer = 300m

v: speed of the person on the car = 6.00 m/s

t=\frac{300m}{6m/s}=50s

4 0
3 years ago
Assume an axon has an internal diameter of 1μm and a myelin sheath 1μm thick. The internal specific resistance is 100 Ω cm. For
SpyIntel [72]

Answer:

1.27\times 10^{12}\Omega/m

Explanation:

We are given that

Diameter=d=\mu m

Thickness=1\mu m

Radius=r=\frac{d}{2}=\frac{1}{2}\mu m=0.5\times 10^{-6} m

Using 1\mu m=10^{-6} m

Dielectric constant=8

Resistance =R=2\times 10^5\Omega cm^2

Internal specific resistance=r=100 ohm cm=100\times \frac{1}{100}\Omega-m=1\Omega m

Using 1 m=100 cm

Internal resistance per unit length=\frac{r}{A}=\frac{1}{\pi r^2}=\frac{1}{3.14\times (0.5\times 10^{-6})^2}=1.27\times 10^{12}\Omega/m

Using \pi=3.14

Internal resistance per unit length=1.27\times 10^{12}\Omega/m

8 0
3 years ago
The "Biltmore Agreement" stipulated that a. remote broadcasts could not emanate from hotels. b. NBC could not give away tickets
Anna35 [415]

Answer:

The "Biltmore Agreement" stipulated that:

Radio stations agreed to broadcast no longer than five minutes of news, twice per day, while using information supplied by the newspapers.

e. radio stations could only air five-minutes newscasts a day.

Explanation:

The Biltmore Agreement tried to reconcile within the press war between newspapers and radio, as during its golden age the newspapers´ revenues decreased. Radio´s brand new technology was more attractive and creative for advertising and could report breaking news faster than the newspapers, which through the press associations including the Associated Press and the United Press, pressured to stop providing news to radio stations beginning a war in 1933, which partially ended with the Biltmore Agreement, which restricted the radio´s broadcasting of news if the newspapers continued publishing radio listings, radio stations were to broadcast no longer than five minutes of news, twice per day, if information supplied by the newspapers was used, no sponsors were allowed, and no more that 30 words in a single story were allowed either;  radio stations had to include: "See your daily newspaper for further details" in their announcements and, could only broadcast news after 9:30 AM for morning news, and after 9:00 PM for evening news, so people would have already received their newspapers.

7 0
3 years ago
a hunter 412.5m from a cliff moves a distance x towards the cliff and fires a gun. he hears the echo from the cliff after 2.2sec
Inessa [10]

Answer: 49.5 m

Explanation:

The speed of sound s is given by a relation between the distance d and the time t:

s=\frac{d}{t} (1)

Where:

s=330 m/s is the speed of sound in air (taking into account this value may vary according to the medium the sound wave travels)

d=412.5 m-x since we are told th hunter was initially 412.5 meters from the cliff and then moves a distance x towards the cliff

t=\frac{2.2 s}{2}=1.1 s Since the time given as data (2.2 s) is the time it takes to the sound wave to travel from the hunter's gun and then go back to the position where the hunter is after being reflected by the cliff

Having this information clarified, let's isolate d and then find x:

d=st (2)

412.5 m-x=(330 m/s)(1.1 s) (3)

Finding x:

x=49.5 m This is the distance at which the hunter is from the cliff.

3 0
3 years ago
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