physics problem
- ashkanOo
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physics problem
A person pushes a stalled 2000 kg car from rest to a speed , doing 4000 J of work in the process. During this time the car moves 20 m. Neglecting friction between the car and the road, find:
a.
the final speed of the car
b.
the horizontal force exerted on the car
a.
the final speed of the car
b.
the horizontal force exerted on the car
B.Sc physics at amirkabir university of tehran
- klausmeister
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Re: physics problem
ashkanisbest نوشته شده:A person pushes a stalled 2000 kg car from rest to a speed , doing 4000 J of work in the process. During this time the car moves 20 m. Neglecting friction between the car and the road, find:
a.
the final speed of the car
b.
the horizontal force exerted on the car
Solution: a)
Consider conservation of energy before and after the push.
Total energy of the system before is equal to the final total energy after, i.e.
m g h + 1/2 m vi^2 = m g h + 1/2 m vf^2
Consider conservation of energy before and after the push.
Total energy of the system before is equal to the final total energy after, i.e.
m g h + 1/2 m vi^2 = m g h + 1/2 m vf^2
m is the mass of the car which is 2000 kg and vi is the initial speed of the car, which is zero.
g is gravitational acceleration of earth and h is the height. Since potential energy for before and after the push does not change, we can cross out that term.
Total initial kinetic energy is zero
So, we are left with final kinetic energy. Because of initial push, we set the final kinetic energy equal to 4000 J and solve for vf.
J=Nm and N=kgm/sec^2
which gives
Solution: b)
Work is defined by w=f.s, where f is the external force exerted on the object and s is the distance the object hast traveled.
Usually, f and s are vectors and the . (dot) in between them is dot or inner product, so that w = f s cos(a). a is the angle between f and s vectors. Now, since f and s are both pointing in the same direction, a is then zero.
So, f is then equal to w/s=4000J/20m=200N.
آخرین ویرایش توسط klausmeister یکشنبه ۱۳۹۱/۶/۵ - ۱۸:۳۱, ویرایش شده کلا 1 بار
- ashkanOo
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Re: physics problem
good
next problem.......
A 100kg vat of fat is pulled across a floor (coefficient of kinetic friction is 0.60) by a massless rope attached to a motor which supplies an average power of 200W. If the vat starts at rest and the motor runs for 4.0s moving it 1.0m, what speed does the vat have at the end of 4.0s?
next problem.......
A 100kg vat of fat is pulled across a floor (coefficient of kinetic friction is 0.60) by a massless rope attached to a motor which supplies an average power of 200W. If the vat starts at rest and the motor runs for 4.0s moving it 1.0m, what speed does the vat have at the end of 4.0s?
B.Sc physics at amirkabir university of tehran
Re: physics problem
Alack
I do not understand what it says
I do not understand what it says
دلا خو کن به تنهایی که از تنها بلا خیزد سعادت آن کسی دارد که از تنها بپرهیزد
درد عشقی کشیدهام که مپرس زهر هجری کشیدهام که مپرس
درد عشقی کشیدهام که مپرس زهر هجری کشیدهام که مپرس
- ashkanOo
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Re: physics problem
m77m نوشته شده:Alack
I do not understand what it says
wait for other problems
B.Sc physics at amirkabir university of tehran
Re: physics problem
SOME word can change the world.,...............
is false
the correct one is some words can change the world
is false
the correct one is some words can change the world
عمري را تلف كردم تا بفهمم فهميدن همه چيز لازم نيست . رنه كوتي
- klausmeister
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Re: physics problem
A 100kg vat of fat is pulled across a floor (coefficient of kinetic friction is 0.60) by a massless rope attached to a motor which supplies an average power of 200W. If the vat starts at rest and the motor runs for 4.0s moving it 1.0m, what speed does the vat have at the end of 4.0s?[/quote]
In this problem we are comparing electrical with mechanical energies.
The average electric power produced by the motor is 200W. Average electric Power is defined as: electric Work/unit time.
The average electric power produced by the motor is 200W. Average electric Power is defined as: electric Work/unit time.
So, the electric work,Welec, put out by the motor for 4 seconds interval is 200W.4 sec=800J.
Units: Watts=Joules/seconds
Next, we look at mechanical energy required to move the vat of fat for 4 seconds.
For some reason the problem has neglected the static friction, and is considering the kinetic frictional force only. The kinetic frictional force is fk = muk Fn = mu m g.
Here fk is kinetic frictional force, muk is coefficient of kinetic friction, Fn is the normal force which is equal in magnitude to m g.
Now, the work, Wfk, is the kinetic frictional force times the distance traveled: Wfk = fk s. This is the energy lost due to friction in the system.
So, Wfk = muk m g s = 0.6 100kg 9.8m/s^2 1m = 588J.
To find the speed of the vat, we subtract work due to friction,Wfk, from the electric work produced by the motor, Welec. the difference is then the kinetic energy of the vat.
(1/2) m v^2 = Welec - Wfk
(1/2) m v^2 = 212J
With m=100kg, v=2.1 m/s
- ashkanOo
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Re: physics problem
false .....
look at this and find ur mistake.....
look at this and find ur mistake.....
شما دسترسی جهت مشاهده فایل پیوست این پست را ندارید.
B.Sc physics at amirkabir university of tehran
- klausmeister
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Re: physics problem
ashkanisbest نوشته شده:false .....
look at this and find ur mistake.....
Your approach is pretty much the same as mine, except for the fact that I have rounded up my answer by one decimal point too much...
Re: physics problem
wich site do u get this problem ?
عمري را تلف كردم تا بفهمم فهميدن همه چيز لازم نيست . رنه كوتي
- ashkanOo
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Re: physics problem
aha okklausmeister نوشته شده:ashkanisbest نوشته شده:false .....
look at this and find ur mistake.....Your approach is pretty much the same as mine, except for the fact that I have rounded up my answer by one decimal point too much...
B.Sc physics at amirkabir university of tehran
- ashkanOo
نام: اشکان
محل اقامت: تهران
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Re: physics problem
A 1400 kg car, heading north and moving at 35 miles per hour collides in a perfectly inelastic collision with a 4000 kg truck going East at 20 miles per hour.
a.
What is the speed and direction of the wrecked vehicles just after collision?
b.
What percentage of the total mechanical energy is lost from the collision?
a.
What is the speed and direction of the wrecked vehicles just after collision?
b.
What percentage of the total mechanical energy is lost from the collision?
B.Sc physics at amirkabir university of tehran
- reza best fizician
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Re: physics problem
it is too good for u undersanding your mistake.say hello to master rezapor
به جای انکه خودت را با دیگران مقایسه کنی خودت را با خودت مقایسه کن_از پسر خاله ام (علی)
- ashkanOo
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Re: physics problem
just say wtf to him......reza best fizician نوشته شده:it is too good for u undersanding your mistake.say hello to master rezapor
B.Sc physics at amirkabir university of tehran