Only for Sc. & (-ngg. nerds and Logic l0vers ...

[MuZammiL Dr. s[1]n]

i thought that it would be an exciting idea to just make a thread in which the P.d.f. members can solve various logical & numerical problems in order to learn and improve their aptitude & understanding of Sc.&Tech. ...

By the way , all geeks n freaks are more than weLLcOme to contribute to any questions & queries put forward here by any keen-to-learn member(s) ...

So i'm bowling the first ball over here ...

Let's get started with this shOt :-

Q.1- 1 gallon of gasoline is used in pulling a load to 10 miles. The force needed to pull the load is 500 pounds. What thermal efficiency does this represent ?

 

[Thirdfront]

i thought that it would be an exciting idea to just make a thread in which the P.d.f. members can solve various logical & numerical problems in order to learn and improve their aptitude & understanding of Sc.&Tech. ...

By the way , all geeks n freaks are more than weLLcOme to contribute to any questions & queries put forward here by any keen-to-learn member(s) ...

So i'm bowling the first ball over here ...

Let's get started with this shOt :-

Q.1- 1 gallon of gasoline is used in pulling a load to 10 miles. The force needed to pull the load is 500 pounds. What thermal efficiency does this represent ?

(10*1.6*9.8*500*.45)/(2.8*43000)=29% (calorific value of petrol taken as 43000 kj/kg and 1 gallon petrol = 2.8 kg)

PS: this is just "Fuel Efficiency". The data is not sufficient to calculate "Thermal" efficiency. Thermal efficiency must be greater than 29%

 

[t_for_talli]

(10*1.6*9.8*500*.45)/(2.8*43000)=29% (calorific value of petrol taken as 43000 kj/kg and 1 gallon petrol = 2.8 kg)

PS: this is just "Fuel Efficiency". The data is not sufficient to calculate "Thermal" efficiency. Thermal efficiency must be greater than 29%

Its not lifting, he asked about pulling object so friction coefficient comes into picture
(10*1.6*9.8*500*.45)= Normal Reaction (N)
((N*coefficient of friction(not given)/(2.8*43000))*100= will give you efficiency(in % terms)

 

[neehar]

efficiency=(output/input energy)

input energy= mass of gasoline x calorific value=vol x density x cal.=1*3.7854*0.75*48000=136.274MJ
output energy=force * distance=500*0.453*9.8*10*1609=35.714MJ
eff=35.714/136.274=0.262=26.2% efficient
converted in to S.I
@MuZammiL Dr. s[1]n

heres mine..consider earth..in which a hole is dug along its diameter through out. now..if u drop an object in the hole..what might happen!!!

 

[HunterKiller]

efficiency=(output/input energy)
heres mine..consider earth..in which a hole is dug along its diameter through out. now..if u drop an object in the hole..what might happen!!!

I think it will be in an endless to-and-fro motion ..

 

[neehar]

1.consider a simple pendulum with a bob of mass m ,and string of length l.it is executing an shm.at it's extreme the height of bob from its mean position is y c.m.and at the mean position it has a velocity of v cm/s.what is the net force on the bob at the mean position?

2.if the bob is filled with water and it has a hole at its bottom will there be any change in its time period if so how??

 

[Sliver]

^^ 1)
The tension equals T = mv^2/r + mg.
(at mean position, there is only centrepetal force)

2) It will first increase in time period then decrease. Cos the center of mass first moves down and them moves up thereby effectively first increasing the length of the pendulum and then decreasing it before finally goes back to the same time period as before the water was there (since the center of mass will now be identical as before).

 

[neehar]

^^ 1)
The tension equals T = mv^2/r + mg.
(at mean position, there is only centrepetal force)

2) It will first increase in time period then decrease. Cos the center of mass first moves down and them moves up thereby effectively first increasing the length of the pendulum and then decreasing it before finally goes back to the same time period as before the water was there (since the center of mass will now be identical as before).

think about the first one carefully i asked the net force.also its cetrefugal force.but ur almost there.

 

[Thirdfront]

Its not lifting, he asked about pulling object so friction coefficient comes into picture
(10*1.6*9.8*500*.45)= Normal Reaction (N)
((N*coefficient of friction(not given)/(2.8*43000))*100= will give you efficiency(in % terms)

Read carefully, he said force required (F) to pull the load, not the load itself. Whether it is lifting, dragging or rolling will not matter.

 

[HunterKiller]

@neehar :

here is mine:

A wave machine consists of two 1 meter length sections of 50 steel rods which are so connected to each other that when the first rod is disturbed from a rest position, the disturbance travels along the medium from rod to rod. One of the sections consists of longer steel rods - disturbance move at 20 cm/s in this section. the other section consists of shorter steel rods - disturbance moves at 80cm/s in this section. If the two two sections are connected together so that pulses can cross the boundary from one section to the other and a pulse of length 10 cm is introduced in the slower section, then what will be the length of the pulse when it crosses the boundary into the faster section....?

 

[Thirdfront]

1.consider a simple pendulum with a bob of mass m ,and string of length l.it is executing an shm.at it's extreme the height of bob from its mean position is y c.m.and at the mean position it has a velocity of v cm/s.what is the net force on the bob at the mean position?

2.if the bob is filled with water and it has a hole at its bottom will there be any change in its time period if so how??

I think it is zero for question 1. Acceleration becomes zero at inflection point and weight is balanced by string tension (if ideal pendulum is assumed).

 

[MuZammiL Dr. s[1]n]

efficiency=(output/input energy)

input energy= mass of gasoline x calorific value=vol x density x cal.=1*3.7854*0.75*48000=136.274MJ
output energy=force * distance=500*0.453*9.8*10*1609=35.714MJ
eff=35.714/136.274=0.262=26.2% efficient
converted in to S.I
@MuZammiL Dr. s[1]n

heres mine..consider earth..in which a hole is dug along its diameter through out. now..if u drop an object in the hole..what might happen!!!

im not sure but just my logical guess is the object would just simply goes on to drop down to the bottom of the earth ...

think about the first one carefully i asked the net force.also its cetrefugal force.but ur almost there.

There is no such force as Centrifugal force , it just simply do not exist because it does not comply to the newton's 3rd law of motion which states that : "action and reaction forces act in pair but they never act on the same body".

 

[neehar]

im not sure but just my logical guess is the object would just simply goes on to drop down to the bottom of the earth ...


There is no such force as Centrifugal force , it just simply do not exist because it does not comply to the newton's 3rd law of motion which states that : "action and reaction forces act in pair but they never act on the same body".

there is no bottom of the earth it oscillates in the hole.

centrifugal force is an apparent force caused on the body because of the velocity of the body.just like when u try to rotate a body in a horizontal circle tension becomes the centrifugal force.in any case the answer is 0 as the net acceleration on the body at the mean position is 0.

@neehar :

here is mine:

A wave machine consists of two 1 meter length sections of 50 steel rods which are so connected to each other that when the first rod is disturbed from a rest position, the disturbance travels along the medium from rod to rod. One of the sections consists of longer steel rods - disturbance move at 20 cm/s in this section. the other section consists of shorter steel rods - disturbance moves at 80cm/s in this section. If the two two sections are connected together so that pulses can cross the boundary from one section to the other and a pulse of length 10 cm is introduced in the slower section, then what will be the length of the pulse when it crosses the boundary into the faster section....?

cudnt visualize buddy can u post a figure?

 

[MuZammiL Dr. s[1]n]

there is no bottom of the earth it oscillates in the hole.

centrifugal force is an apparent force caused on the body because of the velocity of the body.just like when u try to rotate a body in a horizontal circle tension becomes the centrifugal force.in any case the answer is 0 as the net acceleration on the body at the mean position is 0.


cudnt visualize buddy can u post a figure?

no dear, that tension is not the centrifugal force but in fact that tension is generated (due to the weight of a body) as a reactionary force to/against the applied force on the body which is rotating it in a circle ...

you should not mix tension & so-called centrifugal force with each other as the former is a pure force whereas the later one is just an effect felt only in presence of a centripetal force ...

if this reason alone doesn't satisfy you so just try to check whether the centrifugal force conform to newton's 3rd law of motion ...

 

[neehar]

no dear, that tension is not the centrifugal force but in fact that tension is generated (due to the weight of a body) as a reactionary force to/against the applied force on the body which is rotating it in a circle ...

you should not mix tension & so-called centrifugal force with each other as the former is a pure force whereas the later one is just an effect felt only in presence of a centripetal force ...

if this reason alone doesn't satisfy you so just try to check whether the centrifugal force conform to newton's 3rd law of motion ...

as i said centrifugal force is an "apparent force".weight acts vertically downwards.then which force balances the tension????newtons 3rd law also satisfies if the frame of reference is the bob and not earth.its not gravity yes mass comes in to picture because we know mv^2/r.what is the centripetal force in the problem??its the force acting towards the centre which is nothing but tension.to balance it centrifugal force acts outside.