 |
|
|
 |
New Member
|
|
Oct 14, 2010, 09:32 PM
|
|
AP Physics Help on Tension and Energy
An elevator weighing 20000 N is supported by a steel cable. What is the tension in the cable when the elevator is being accelerated upaward at a rate of 3.00 m/s squared.
I don't understand on how to find tesion and I have a test tomorrow and I have a lot of questions so I hope you guys can help me on this and other problems that involve energy :)
Thx
|
|
 |
Expert
|
|
Oct 15, 2010, 05:36 AM
|
|
ΣF=ma is at work here. You know the mass of the elevator cab, you have been told what the value of its acceleration is, so with ΣF=ma you can calculate the net force needed to make it accelerate upward. That net force equals the upward force of the tension in the cable minus the downward force of the weight of the elevator cab. Can you take it from here?
|
|
 |
Junior Member
|
|
Oct 15, 2010, 06:38 AM
|
|
 Originally Posted by ebaines
ΣF=ma is at work here. You know the mass of the elevator cab, you have been told what the value of its acceleration is, so with ΣF=ma you can calculate the net force needed to make it accelerate upward. That net force equals the upward force of the tension in the cable minus the downward force of the weight of the elevator cab. Can you take it from here?
If the elevator is going up the wouldn't the forces be added together instead of subtracted? The tension is greater when the elevator is moving up than it is at rest just hanging. So, if it is going up, it had to overcome gravity making the net acceleration gravity plus 3m/s^2. This makes the force equal to the mass times gravity plus 3. Thus F=(20000/9.8)(9.8+3). Because it gives you the force while at rest, you divide that by gravity, giving you the mass, m=F/a, then multiply the mass by the total acceleration of 12.3m/s^2. Your answer would be correct if the question asked for the upward force of the elevator, not the tension in the cable. Hope this helps!
|
|
 |
Uber Member
|
|
Oct 15, 2010, 07:01 AM
|
|
I used both of your answers, ebaines and kpg0001, and I get the same answer. So, both ways work, if you know what you are doing.
|
|
 |
Expert
|
|
Oct 15, 2010, 07:17 AM
|
|
 Originally Posted by kpg0001
If the elevator is going up the wouldn't the forces be added together instead of subtracted?
The math goes like this: let  = tension in the cable, and  = weight of the elevator, then
So yes, the tension works out to be the sum of the weight plus the force needed to accelerate the elevator cab, but it is derived from ΣF = Force of tension MINUS the weight.
|
|
Question Tools |
Search this Question |
|
|
Add your answer here.
Check out some similar questions!
Physics, conservation of machanical energy?
[ 1 Answers ]
A 0.45-kg ball was kicked straight up with an initial speed of 18 m/s. The ball reached a height that is 80% of the height that would have been reached had there been no air resistance.
(a) Use the law of conservation of energy to calculate the work done on the ball, on its way up, by the force...
Physics, The Work-ENERGY
[ 1 Answers ]
A space ship of mass 5.00 × 18*4 kg is traveling at a speed 1.15 × 10*4 m/s in outer
space. Except for the force generated by its own engine, no other force acts on
the ship. As the engine exerts a constant force of 4.00 × 10*5 N, the ship moves a
distance of 2.50 × 10*6 m in the direction of...
Physics, The Work-Energy PRINCIPLE
[ 1 Answers ]
A 25-kg box slides, from rest, down a 9.0-m-long incline that makes an angle of
15° with the horizontal. The speed of the box when it reaches the bottom of the
Incline is 2.4 m/s.
(a) What is the coefficient of kinetic friction between the box
And the surface of the incline?
(b) How much...
Physics (Conservation of Energy)
[ 1 Answers ]
A 100g arrow is pulled back 75cm with an average force of 290N, aimed upwards, and released. Use the law of conservation of energy to solve these problems.
a) Neglecting air resistance, how high should the arrow go?
b) If the arrow went up 149m, how much work was done against air resistance?...
Momentum,energy physics
[ 2 Answers ]
Please could you help me with these problems..Thanks in advance for your help.
14.) A person moves a large box across a level floor by applying a horizontal force of 300 N. If the person pushes the box a distance of 6 meters in 10 seconds, how much work does the person do on the box?a. 180...
View more questions
Search
|