죽기 전에 > 건강한 뇌 만들기 > 건강한 뇌 만들기 운동(290)

	총 게시물 182건, 최근 0 건

건강한 뇌 만들기 운동(290)

글쓴이 : yu41pak 날짜 : 2016-07-23 (토) 08:19 조회 : 1274

===

뇌는 쓸수록 건강해진다.

뇌가 건강치 못하면 아무 것도 건강치 못하게 된다.

옳고 그름을

바로 보고 바로 판단하고 바로 옮길 수 있어야 건강한 바른 삶이 된다.--

---------*----------------*------------------------

<제 056 회> 자전거

[문] :

어떤 자전거가 일정한 언덕을

시간당 10마일 속력으로 올라가고

시간당 20마일로 돌아온다.

전체주행에 소요되는 자전거의 평균속력은 얼마일까요?

보기 :

가) 12 mph 나) 12 1/3 " 다) 13 1/3 " 라) 13 2/3 "

[답] ( )

--------------------------------- *정답은 다음 회에 있습니다.

[Q] :

A bicycle climbs a certain hill at 10 miles an hour

and return at 20 miles an hour.

What is its average speed for the entire trip ?

---------------------------------------------------------

지난 회 <제 065 회> 어떻게 도망을 가나?

[문] :

상상을 해보자!

당신은 방문도 없고, 창문도 없고,

아무데고 나갈 길이 없는 방에 있다하자.

그 방안엔 사자 한 마리가 있어 당신을 잡아먹으려 한다.

당신은 어떻게 도망을 가겠나?

---------------------------------------------------------

지난 회 [제 065 회 정답 및 해설]

정답 : 라) 여기선 말 못 하지만 길이 있다.

해설 :

상상을 멈추라! / Stop imaging!

--------------------------------------------------------

--- 오늘도 좋은 하루 건강한 하루가 되시기 바랍니다. ---

--------------------------------------------------------

이태백

2016-07-23 (토) 11:57

모르는 거리와 그 모르는 시간을 빼버리고 계산하기.

속도=거리/시간

=왕복길이/왕복시간

=2x출발점에서 언덕까지의 길이/올라갈 때까지 시간+내려올 때의 시간

=2x출발점에서 언덕까지의 길이／언덕까지의 길이/올라간 속도+'언덕까지의길이'/'내려온 속도'

이 것을 정리하여 GMAT Avenger Study Group이 아래와 같이 정리하여

2x 올라간 속도x 내려오는 속도 /올라간 시간+내려온 시간

= 2x(10x20)/10+20

=400÷30

=13.33

댓글주소

<div>모르는 거리와 그 모르는 시간을 빼버리고 계산하기.</div><div> </div>속도=거리/시간<div>=왕복길이/왕복시간<div>=2x출발점에서 언덕까지의 길이/올라갈 때까지 시간+내려올 때의 시간</div><div>=2x출발점에서 언덕까지의 길이／언덕까지의 길이/올라간 속도+'언덕까지의길이'/'내려온 속도'</div><div>이 것을 정리하여 GMAT Avenger Study Group이 아래와 같이 정리하여</div><div>2x 올라간 속도x 내려오는 속도 /올라간 시간+내려온 시간</div><div>= 2x(10x20)/10+20&nbsp;</div><div>=400÷30</div><div>=13.33</div><div> </div></div>

이태백

2016-07-23 (토) 11:58

골치 아프게 생각해도 이해가 안감. ^-^

댓글주소

이태백

2016-07-23 (토) 12:17

누가 평균속도 공식

올라갈 때의 속도:R₁

내려올 때의 속도:R₂라 할 때에

V=[2(R₁)(R₂)/[R₁+R₂]를 만들었는지 찾지 못했음.

V=[2(10)(20)/[10+20]=400/30=13.33 miles

이 건 분명히 답이 10~20 사이에 있을 것이라는 가정하에 통계적으로 꾸어맞춘 공식이 아닌지.

까닭은 위의 공식을 유도해낼 수가 없기에.

댓글주소

써니

2016-07-24 (일) 01:14

[답] 다)

업 속도 10마일

다운 속도 20마일 인데

예를 들어 거리가 10마일 이라면

올라가는 데 1 시간 걸리고

내려오는 데 반시간 걸린다면

그러면 20마일 가는데 1시간 반

그러므로 속도는 시속 13 과 1/3 마일

참고로 ........................

Forces and Power

The figure below shows a bicycle going uphill at an angle of inclination Φ, and with a velocity V.

bicycle going up incline

To propel the bicycle uphill the rider must push down on the pedals. The pedals are offset 180° which means that only one pedal can be pushed at a time, from the top position to the bottom position, and then switching to the other pedal.

Given a force F₁ acting on the pedal we can calculate the resulting force F₄between the rear wheel and ground. This is the force that propels the bicycle forward.

We can perform a torque analysis with good accuracy based on the assumption that acceleration (linear and angular) is negligible. Hence, we can treat this as a static problem.

Consider the figure below, with forces and radial dimensions shown.

rear bicycle wheel 1

Where:

F₁ is the force applied to the pedal

R₁ is the pedal radius

F₂ is the force acting on the main crank, due to chain contact

R₂ is the main crank radius

F₃ is the force acting on the rear gear, due to chain contact

R₃ is the rear gear radius

F₄ is the force acting on the rear wheel, due to contact with the ground. Note that the coefficient of static friction between wheel and ground must be large enough to support this force, otherwise slipping occurs

R₄ is the rear wheel radius

Using the static equilibrium assumption, we can write the following torque equations:

and

Since F₂ = F₃, we can combine the above two equations to give an __EXPRESSION__ for F₄:

rear wheel force for bike based on torque

The force F₄ is what propels the bicycle forward. If we assume that the bicycle is moving at constant velocity (no acceleration) then the force F₄must equal the resisting forces opposing the bicycle's motion. These resisting forces are gravity, rolling resistance, air drag, and internal bicycle friction. If we neglect the latter we can then write the following mathematical __EXPRESSION__:

push force eqn for bike going up hill with rolling and air drag

push force eqn for bike going up hill with rolling and air drag

Where:

F is the force propelling the bicycle forward. Note that F ≡ F₄

C_r is the coefficient of rolling resistance, which can be 0.0022 to 0.005 for bicycle tires (ref: http://en.wikipedia.org/wiki/Rolling_resistance)

C_d is the drag coefficient

ρ is the density of the air through which the bicycle is moving

A is the projected cross-sectional area of the bike+rider perpendicular to the flow direction (that is, perpendicular to v), and v is the speed of the bicycle relative to the air

The first term on the right side of the above equation is the gravity contribution. The second term is the rolling resistance contribution. The third term is the air drag contribution.

To evaluate the power P required to propel the bicycle, multiply the above equation by v. We get P = Fv, and

push power eqn for bike going up hill with rolling and air drag

push power eqn for bike going up hill with rolling and air drag

For a flat surface (no incline) set Φ = 0. We get

push force for bike on level surface with rolling and air drag

and

push power for bike on level surface with rolling and air drag

We can also solve for the terminal velocity of a bicycle coasting down a hill with given inclination angle of Φ. Since the rider in this case does not exert any force on the pedals, we have F ≡ F₄ = 0. Hence, the force of gravity must balance the resistive forces due to rolling resistance and air drag. Hence, we can solve for the terminal coasting velocity v in the following equation:

force eqn for bike coasting down hill with rolling and air drag

force eqn for bike coasting down hill with rolling and air drag

Naturally, when riding a bike we wish to keep resistive forces opposing motion as low as possible. This is accomplished by keeping the tires well pressurized (which minimizes rolling resistance) and keeping the frontal area A as small as possible to reduce air drag, especially when traveling at high speeds, such as in a race. Typically, the rolling resistance is much higher than air drag so reducing A is not important for the average rider who travels at moderate speeds.

A Fun Experiment

Try out this fun experiment related to bicycle physics (shown below). Stand a bicycle upright and orient one of the pedals so that it's at the bottom position. Next, push left on the pedal. Which way does the bicycle move?

rear bicycle wheel 2

Answer: The bicycle moves to the left (which might be non-intuitive to you). Even though the force you are applying to the pedal turns the main crank clockwise, which is the direction required to move the bike to the right, the bicycle ends up moving left. This is because the external force F₁you are applying to the bike, results in a lesser force F₄ in the opposite direction. Since F₁ > F₄, the bicycle moves left. Now, if you were to sit on the bike and apply a force F₁ with your foot, the bicycle would move to the right since F₁ is now an internal force in the bike-rider system and hence the only external force acting on the bicycle is F₄ acting on the rear wheel, which pushes the bicycle to the right.

댓글주소

<div> </div><div>[답] &nbsp;다)</div><div> </div><div>업 속도 10마일&nbsp;</div><div>다운 속도 20마일 인데</div><div> </div><div>예를 들어 거리가 &nbsp;10마일 이라면</div><div> </div><div>올라가는 데 1 시간 걸리고</div><div>내려오는 데 반시간 걸린다면</div><div>그러면&nbsp;20마일 가는데 1시간 반</div><div> </div><div>그러므로 속도는 시속 13 과 1/3 마일&nbsp;</div><div> </div><div> </div><div> </div><div>참고로 ........................</div><div> </div><div> </div><div> </div><div>Forces and Power&nbsp; The figure below shows a bicycle going uphill at an angle of inclination&nbsp;Φ, and with a velocity&nbsp;V.&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_3.png" width="437" height="442" alt="bicycle going up incline" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; To propel the bicycle uphill the rider must push down on the pedals. The pedals are offset 180° which means that only one pedal can be pushed at a time, from the top position to the bottom position, and then switching to the other pedal.&nbsp; Given a force&nbsp;F1&nbsp;acting on the pedal we can calculate the resulting force&nbsp;F4between the rear wheel and ground. This is the force that propels the bicycle forward.&nbsp; We can perform a torque analysis with good accuracy based on the assumption that acceleration (linear and angular) is negligible. Hence, we can treat this as a static problem.&nbsp; Consider the figure below, with forces and radial dimensions shown.&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_4.png" width="492" height="377" alt="rear bicycle wheel 1" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; Where:&nbsp; F1&nbsp;is the force applied to the pedal&nbsp; R1&nbsp;is the pedal radius&nbsp; F2&nbsp;is the force acting on the main crank, due to chain contact&nbsp; R2&nbsp;is the main crank radius&nbsp; F3&nbsp;is the force acting on the rear gear, due to chain contact&nbsp; R3&nbsp;is the rear gear radius&nbsp; F4&nbsp;is the force acting on the rear wheel, due to contact with the ground. Note that the coefficient of static friction between wheel and ground must be large enough to support this force, otherwise slipping occurs&nbsp; R4&nbsp;is the rear wheel radius&nbsp; Using the static equilibrium assumption, we can write the following torque equations:&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_11.png" width="142" height="43" alt="torque for bike 1" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; and&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_12.png" width="144" height="44" alt="torque for bike 2" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; Since&nbsp;F2&nbsp;=&nbsp;F3, we can combine the above two equations to give an expression for&nbsp;F4:&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_13.png" width="154" height="78" alt="rear wheel force for bike based on torque" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; The force&nbsp;F4&nbsp;is what propels the bicycle forward. If we assume that the bicycle is moving at constant velocity (no acceleration) then the force&nbsp;F4must equal the resisting forces opposing the bicycle's motion. These resisting forces are gravity, rolling resistance, air drag, and internal bicycle friction. If we neglect the latter we can then write the following mathematical expression:&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_18.png" width="432" height="80" alt="push force eqn for bike going up hill with rolling and air drag" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; Where:&nbsp; F&nbsp;is the force propelling the bicycle forward. Note that&nbsp;F&nbsp;≡&nbsp;F4&nbsp; Cr&nbsp;is the coefficient of rolling resistance, which can be 0.0022 to 0.005 for bicycle tires (ref: http://en.wikipedia.org/wiki/Rolling_resistance)&nbsp; Cd&nbsp;is the drag coefficient&nbsp; ρ&nbsp;is the density of the air through which the bicycle is moving&nbsp; A&nbsp;is the projected cross-sectional area of the bike+rider perpendicular to the flow direction (that is, perpendicular to&nbsp;v), and&nbsp;v&nbsp;is the speed of the bicycle relative to the air&nbsp; The first term on the right side of the above equation is the gravity contribution. The second term is the rolling resistance contribution. The third term is the air drag contribution.&nbsp; To evaluate the power&nbsp;P&nbsp;required to propel the bicycle, multiply the above equation by&nbsp;v. We get&nbsp;P&nbsp;=&nbsp;Fv, and&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_19.png" width="464" height="76" alt="push power eqn for bike going up hill with rolling and air drag" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; For a flat surface (no incline) set&nbsp;Φ&nbsp;= 0. We get&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_15.png" width="250" height="83" alt="push force for bike on level surface with rolling and air drag" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; and&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_16.png" width="316" height="77" alt="push power for bike on level surface with rolling and air drag" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; We can also solve for the terminal velocity of a bicycle coasting down a hill with given inclination angle of&nbsp;Φ. Since the rider in this case does not exert any force on the pedals, we have&nbsp;F&nbsp;≡&nbsp;F4&nbsp;= 0. Hence, the force of gravity must balance the resistive forces due to rolling resistance and air drag. Hence, we can solve for the terminal coasting velocity&nbsp;v&nbsp;in the following equation:&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_17.png" width="385" height="81" alt="force eqn for bike coasting down hill with rolling and air drag" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; Naturally, when riding a bike we wish to keep resistive forces opposing motion as low as possible. This is accomplished by keeping the tires well pressurized (which minimizes rolling resistance) and keeping the frontal area&nbsp;A&nbsp;as small as possible to reduce air drag, especially when traveling at high speeds, such as in a race. Typically, the rolling resistance is much higher than air drag so reducing&nbsp;A&nbsp;is not important for the average rider who travels at moderate speeds.&nbsp; A Fun Experiment&nbsp; Try out this fun experiment related to bicycle physics (shown below). Stand a bicycle upright and orient one of the pedals so that it's at the bottom position. Next, push left on the pedal. Which way does the bicycle move?&nbsp; <img src="http://www.real-world-physics-problems.com/images/bicycle_physics_5.png" width="468" height="429" alt="rear bicycle wheel 2" style="border: none; max-width: none; font-family: SourceSansPro, Arial, Helvetica, sans-serif; font-size: 16px; line-height: 24px;">&nbsp; Answer: The bicycle moves to the left (which might be non-intuitive to you). Even though the force you are applying to the pedal turns the main crank clockwise, which is the direction required to move the bike to the right, the bicycle ends up moving left. This is because the external force&nbsp;F1you are applying to the bike, results in a lesser force&nbsp;F4&nbsp;in the opposite direction. Since&nbsp;F1&nbsp;&gt;&nbsp;F4, the bicycle moves left. Now, if you were to sit on the bike and apply a force&nbsp;F1&nbsp;with your foot, the bicycle would move to the right since&nbsp;F1&nbsp;is now an internal force in the bike-rider system and hence the only external force acting on the bicycle is&nbsp;F4&nbsp;acting on the rear wheel, which pushes the bicycle to the right.&nbsp;</div><div> </div><div> </div><div> </div><div> </div>

이태백

2016-07-24 (일) 03:29

.........

20마일 가는데 한 시간 반.

그러므로 13⅓마일 ← 이 '그러므로'를 이해하지 못한다는 겁니다. ^-^ dkp

댓글주소

	총 게시물 182건, 최근 0 건


제목	조회

건강한 뇌 만들기 - 연재 +1	2927

박 서방의 인사 글(고(故) 박경용 선생의 영전… +1	2178

건강한 뇌 만들기 운동(296) +2	2338

건강한 뇌 만들기 운동(295) +1	2416

건강한 뇌 만들기 운동(294) +2	2416

건강한 뇌 만들기 운동(293) +1	2230

건강한 뇌 만들기 운동(292) +2	1081

건강한 뇌 만들기 운동(291) +2	1105

건강한 뇌 만들기 운동(290) +5	1275

건강한 뇌 만들기 운동(289) +3	1255

건강한 뇌 만들기 운동(288) +4	1209

건강한 뇌 만들기 운동(287) +4	1299

건강한 뇌 만들기 운동(286) +2	1167

건강한 뇌 만들기 운동(285) +1	1086

건강한 뇌 만들기 운동(284 +2	1175

건강한 뇌 만들기 운동(283) +3	1270

건강한 뇌 만들기 운동(282) +2	1169

건강한 뇌 만들기 운동(281) +2	1229

건강한 뇌 만들기 운동(280) +2	1272

건강한 뇌 만들기 운동(279) +2	1269

건강한 뇌 만들기 운동(278) +5	1413

건강한 뇌 만들기 운동(277) +10	1769

건강한 뇌 만들기 운동(276) +3	1380

건강한 뇌 만들기 운동(275) +2	1167

건강한 뇌 만들기 운동(274) +1	1214

건강한 뇌 만들기 운동(273) +1	1115

건강한 뇌 만들기 운동(272) +2	1251

건강한 뇌 만들기 운동(271) +3	1210

건강한 뇌 만들기 운동(270) +2	1219

-건강한 뇌 만들기 운동(269) +1	1285

-건강한 뇌 만들기 운동(268) +2	1234

1 2 3 4 5 6 7 맨끝

백세넷 http://100se.net E-mail: 100se.net.mail@gmail.com

맨위로