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3 years ago

A machine has an efficiency of 70%. How much work dose the machine do when 20,000 J of work is done on it

Physics

1 answer:

hram777 [196]3 years ago

3 0

If the machine works at a 70% efficiency it must complete 14,000 work out of the 20,000

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A fireman is sliding down a fire pole. As he speeds up, he tightens his grip on the pole, thus increasing the vertical frictiona

Andrei [34K]

Answer:

The fireman will continue to descend, but with a constant speed.

Explanation:

In kinetic friction (which is the case discussed here) since the fireman is already in motion because of a certain force, once the frictional force matches the normal force, the fireman will stop accelerating and continue moving at a constant rate with the original speed he had. We will need a force greater than the normal force acting on the fireman to cause a deceleration.

We need to understand the difference between static friction and kinetic friction.

Static friction occurs in objects that are stationary, while kinetic friction occurs in objects that are already in motion.

In static friction, when the frictional force matches the weight or normal force of the object, the object remains stationary.

While in kinetic friction, when the frictional force matches the normal force, the object will stop accelerating. This is the case of the fireman sliding down the pole as discussed above.

8 0

3 years ago

A 4000 kg satellite is placed 2.60 x 10^6 m above the surface of the Earth.

mash [69]

a) The acceleration of gravity is $4.96 m/s^2$

b) The critical velocity is 6668 m/s (24,006 km/h)

c) The period of the orbit is 8452 s

d) The satellite completes 10.2 orbits per day

e) The escape velocity of the satellite is 9430 m/s

f) The escape velocity of the rocket is 11,191 m/s

Explanation:

The acceleration of gravity for an object near a planet is given by

$g=\frac{GM}{(R+h)^2}$

where

G is the gravitational constant

M is the mass of the planet

R is the radius of the planet

h is the height above the surface

In this problem,

$M=5.98\cdot 10^{24} kg$ (mass of the Earth)

$R=6.37\cdot 10^6 m$ (Earth's radius)

$h=2.60\cdot 10^6 m$ (altitude of the satellite)

Substituting,

$g=\frac{(6.67\cdot 10^{-11})(5.98\cdot 10^{24}}{(6.37\cdot 10^6 + 2.60\cdot 10^6)^2}=4.96 m/s^2$

The critical velocity for a satellite orbiting around a planet is given by

$v=\sqrt{\frac{GM}{R+h}}$

where we have again:

$M=5.98\cdot 10^{24} kg$ (mass of the Earth)

$R=6.37\cdot 10^6 m$ (Earth's radius)

$h=2.60\cdot 10^6 m$ (altitude of the satellite)

Substituting,

$v=\sqrt{\frac{(6.67\cdot 10^{-11})(5.98\cdot 10^{24}}{(6.37\cdot 10^6 + 2.60\cdot 10^6)}}=6668 m/s$

Converting into km/h,

$v=6668 m/s \cdot \frac{3600 s/h}{1000 m/km}=24,006 km/h$

The period of the orbit is given by the circumference of the orbit divided by the velocity:

$T=\frac{2\pi (R+h)}{v}$

where

$R=6.37\cdot 10^6 m$

$h=2.60\cdot 10^6 m$

v = 6668 m/s

Substituting,

$T=\frac{2\pi (6.37\cdot 10^6 + 2.60\cdot 10^6)}{6668}=8452 s$

One day consists of:

$t = 24 \frac{hours}{day} \cdot 60 \frac{min}{hours} \cdot 60 \frac{s}{min}=86400 s$

While the period of the orbit is

T = 8452 s

So, the number of orbits completed by the satellite in one day is

$n=\frac{t}{T}=\frac{86400}{8452}=10.2$

The escape velocity for an object in the gravitational field of a planet is given by

$v=\sqrt{\frac{2GM}{R+h}}$

where here we have:

$M=5.98\cdot 10^{24} kg$

$R=6.37\cdot 10^6 m$

$h=2.60\cdot 10^6 m$

Substituting, we find

$v=\sqrt{\frac{2(6.67\cdot 10^{-11})(5.98\cdot 10^{24}}{(6.37\cdot 10^6 + 2.60\cdot 10^6)}}=9430 m/s$

We can apply again the formula to find the escape velocity for the rocket:

$v=\sqrt{\frac{2GM}{R+h}}$

Where this time we have:

$M=5.98\cdot 10^{24} kg$

$R=6.37\cdot 10^6 m$

$h=0$ , because the rocket is located at the Earth's surface, so its altitude is zero.

And substituting,

$v=\sqrt{\frac{2(6.67\cdot 10^{-11})(5.98\cdot 10^{24}}{(6.37\cdot 10^6)}}=11,191 m/s$

Learn more about gravitational force:

brainly.com/question/1724648

brainly.com/question/12785992

#LearnwithBrainly

6 0

3 years ago

To understand the terms in Faraday's law and to be able to identify the magnitude and direction of induced emf. Faraday's law st

wlad13 [49]

Answer: $V_{\epsilon}\propto \frac{d\phi_{B}}{dt}$

Explanation:

A direct proportionality means a linear relationship between two variables and rate of change means an application of derivatives. Hence, the mathematical model is:

$V_{\epsilon}\propto \frac{d\phi_{B}}{dt}$

5 0

3 years ago

All of the following are part of the electromagnetic spectrum but

Lera25 [3.4K]

D)sound waves the electromagnetic spectrum has to do with colors

3 0

3 years ago

Read 2 more answers

An elephant and a mouse would both have zero weight in gravity-free space. If they were moving toward you with the same speed, w

Dovator [93]

The elephant and the mouse having zero weight in a gravity free space will not bump into you at the same effect.

Explanation: 

When both are in a gravity free space, the weights are zero, as we know that the $\text {weight of the body}=\text {mass of the body} \times \text {acceleration due to gravity}$

$\text {here, the weight of elephant}=\text {mass of elephant } \times \text {zero gravti} y=zero$

$\text {similarly,weight of mouse}=\text {mass of mouse } \times \text {zero gravity}=zero$

But when they will acquire the speed of same magnitude, say v, their different masses will acquire different momentum, which will make the difference in effect while bumping.

$\text { momentum of elephant }=\text { mass of elephant } \times v$ $\text { momentum of mouse = mass of mouse } \times v$

And as we know $\text { mass of elephant }>\text { mass of mouse }$ Therefore, effect of impact by elephant will be more than that of mouse . An elephant breaking into you will take you back faster than a mouse in space hits you.

8 0

3 years ago