A train travels 92 miles in 11 1/2 hours. what is its average speed in miles per hour?

A heavy solid disk rotating freely and slowed only by friction applied at its outer edge takes 120 seconds to come to a stop.

alisha [4.7K]

Answer:

The time is 16 min.

Explanation:

Given that,

Time = 120 sec

We need to calculate the moment of inertia

Using formula of moment of inertia

$I=\dfrac{1}{2}MR^2$

If the disk had twice the radius and twice the mass

The new moment of inertia

$I'=\dfrac{1}{2}\times2M\times(2R)^2$

$I'=8I$

We know,

The torque is

$\tau=F\times R$

We need to calculate the initial rotation acceleration

Using formula of acceleration

$\alpha=\dfrac{\tau}{I}$

Put the value in to the formula

$\alpha=\dfrac{F\times R}{\dfrac{1}{2}MR^2}$

$\alpha=\dfrac{2F}{MR}$

We need to calculate the new rotation acceleration

Using formula of acceleration

$\alpha'=\dfrac{\tau}{I'}$

Put the value in to the formula

$\alpha=\dfrac{F\times R}{8\times\dfrac{1}{2}MR^2}$

$\alpha=\dfrac{2F}{8MR}$

$\alpha=\dfrac{\alpha}{8}$

Rotation speed is same.

We need to calculate the time

Using formula angular velocity

$\Omega=\omega'$

$\alpha\time t=\alpha'\times t'$

Put the value into the formula

$\alpha\times120=\dfrac{\alpha}{8}\times t'$

$t'=960\ sec$

$t'=16\ min$

Hence, The time is 16 min.

5 0

3 years ago

By the 2nd century BCE the ____ democratized astrology<br> A. Greeks<br> B. Egyptians<br> C. Romans

elena-14-01-66 [18.8K]

Answer:

A

Explanation:

3 0

3 years ago

HELP PLZ ASAP!!

Andre45 [30]

1. The successful launch of communication satellites

2.More people will be interested in studying science

But science would probably be focused on space exploration and there will probably be less scientists in other fields such as chemistry.

5 0

3 years ago

A refrigerator with a weight of 1,127 newtons needs to be moved into a house using a ramp. The length of the ramp is 2.1 meters,

mestny [16]

The used work of energy output is 496*2.1=1041.6 J. And the actual work of energy output is 1127*0.85=957.95 J. The percentage efficiency is 957.95/1041.6*100%=91.97 %.

3 0

3 years ago

Read 2 more answers

The height of an object is 10 cm, and the height of its image is 6 cm. What is the magnification?

kipiarov [429]

magnification = $\bf\dfrac{height of image}{height of object}$

= $\bf\dfrac{6cm}{10cm}$

= 0.6

3 0

2 years ago