- #1
notsam
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In summary, the problem is that the user is trying to calculate the net acceleration experienced by a mass (in this case, a passenger in an elevator) and is getting incorrect results because of a mistake in the calculation of the acceleration.
- #2
PhanthomJay
Science Advisor
Homework Helper
Gold Member
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When you find the acceleration of the system and multiply it by the mass, you get the NET force acting on the object. The NET force consists of the elevator weight and the cord tension. You want to solve for the tension. Please try again. And welcome to PF!
- #3
notsam
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Thank you very much, as I said before, "I thought that it would be as simple as finding the net acceleration in the system, and then multiplying it by the mass. Unforunatlly I can not come up with the right awnser." But unfortunatly the awnser isn't cooperating with the UTEID quest online homework that I am plugging it into, an awnser or step by step process would be very much appreciated.
- #4
notsam
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- 0
My awnser is 71.76. Even knowing if this is correct or not would be a big help
- #5
gneill
Mentor
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The problem description is lacking certain details. For example, are we to assume that there is an elevator, and inside the elevator is a mass of 9.2kg suspended by a cord affixed to the elevator ceiling, and you want the tension in that cord as the elevator accelerates? Also, is the elevator motion upwards or downwards?
- #6
notsam
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"An elevator starts from rest with a constant
upward acceleration andmoves 1m in the first
1.6 s. A passenger in the elevator is holding a
9.2 kg bundle at the end of a vertical cord.
The acceleration of gravity is 9.8 m/s2 .
What is the tension in the cord as the ele-
vator accelerates? Give your awnser in N"
Again the awnser that I am getting is 71.76 and my net acceleration is -7.8 m/s squared
upward acceleration andmoves 1m in the first
1.6 s. A passenger in the elevator is holding a
9.2 kg bundle at the end of a vertical cord.
The acceleration of gravity is 9.8 m/s2 .
What is the tension in the cord as the ele-
vator accelerates? Give your awnser in N"
Again the awnser that I am getting is 71.76 and my net acceleration is -7.8 m/s squared
- #7
gneill
Mentor
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Okay, that's more clear. The elevator is accelerating upwards, which means that the reaction force on the bundle will be in the downwards direction, adding to the force of gravity and making the bundle heavier (more tension in the cord). Your answer seems to be a bit low.
Can you show us how you calculated the acceleration rate for the elevator?
Can you show us how you calculated the acceleration rate for the elevator?
- #8
notsam
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I used basic kinimatic equations to calculate my acceleration. Using D=1 m t=1 s and Vi= 0 m/s. I calculated the Vf to be 2 m/s, using D= (Vi+Vf/2) t. After that I calculated my acceleration to be 2 m/s2, using Vf=Vi +at. So I'm guessing that I should add my acceleration to garvity instead of subtracting, it and that will give me the correct net acceleration?
- #9
gneill
Mentor
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Okay, your acceleration is off. I'm assuming that you're using Vi = 0, then
D = (Vf/2)*t, so that Vf = 2*D/t giving Vf = 1.25 m/s rather than your 2 m/s. That will affect your acceleration result.
You are right that you'll have to add your acceleration to the acceleration due to gravity in order to determine the net acceleration experienced by the bundle.
D = (Vf/2)*t, so that Vf = 2*D/t giving Vf = 1.25 m/s rather than your 2 m/s. That will affect your acceleration result.
You are right that you'll have to add your acceleration to the acceleration due to gravity in order to determine the net acceleration experienced by the bundle.
- #10
notsam
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- 0
Ohhhhh my problem is I can't multiply apprently...that's embarasing. Thank you very much :) This was definitely the easiest problem and I couldn't figure out what I was doing wrong
FAQ: Tension on a moving cord (Elevator)
What is tension in relation to a moving cord?
Tension is a force that is exerted on a cord or rope when it is pulled from both ends. In the context of an elevator, tension is the force required to lift or lower the elevator car.
How does the tension on a moving cord affect the elevator?
The tension on a moving cord is what allows the elevator to move up or down. When the tension is greater than the weight of the elevator car and its occupants, it will rise. When the tension is less than the weight, the elevator will lower.
What factors affect the tension on a moving cord in an elevator?
The tension on a moving cord is affected by the weight of the elevator and its occupants, as well as the speed and acceleration of the elevator. The angle at which the cord is pulled and any friction or resistance in the pulley system can also impact the tension.
Can the tension on a moving cord be too high?
Yes, the tension on a moving cord can be too high. If the tension exceeds the breaking strength of the cord, it can snap and cause the elevator to freefall. This is why elevators are equipped with safety mechanisms to prevent this from happening.
How is the tension on a moving cord in an elevator calculated?
The tension on a moving cord can be calculated using Newton's second law of motion, which states that force is equal to mass times acceleration. In this case, the force is the tension, and the mass and acceleration can be determined using the weight and movement of the elevator.