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- Jul 25, 2016
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Hey all,
I'm having a lot of trouble working through this physics question from coursesaver, mostly because I don't think the algebra of the solution is quite right:
A 2000kg elevator is connected to a cable. What is the tension in the cable when the elevator is accelerating downward at the rate of 1.5 m/s2? (Approximate the acceleration due to gravity as 10m/s2)
The solution is listed as:
The components of the net force, FNET, for the elevator are tension, T, and weight, W:
FNET = T W = ma
Substitute in the weight: W = mg = (2000kg)(10m/s2) = 20,000N
* Note, the acceleration of 1.5m/s2 is negative since the acceleration is downwards.
T 20,000N = (2000kg)(-1.5m/s2)
T 20,000N = -3000N
T = -3000N + 20,000N = 17,000N
I'm not sure here if FNET = T W = ma should be T+W or T-W. I'm guessing it's T-W, as that's how the algebra works out. Can someone clarify for me? I though weight and tension would be working in the same direction?
I'm getting really discouraged because even going over physics every day doesn't seem to be helping me... argh.
I'm having a lot of trouble working through this physics question from coursesaver, mostly because I don't think the algebra of the solution is quite right:
A 2000kg elevator is connected to a cable. What is the tension in the cable when the elevator is accelerating downward at the rate of 1.5 m/s2? (Approximate the acceleration due to gravity as 10m/s2)
The solution is listed as:
The components of the net force, FNET, for the elevator are tension, T, and weight, W:
FNET = T W = ma
Substitute in the weight: W = mg = (2000kg)(10m/s2) = 20,000N
* Note, the acceleration of 1.5m/s2 is negative since the acceleration is downwards.
T 20,000N = (2000kg)(-1.5m/s2)
T 20,000N = -3000N
T = -3000N + 20,000N = 17,000N
I'm not sure here if FNET = T W = ma should be T+W or T-W. I'm guessing it's T-W, as that's how the algebra works out. Can someone clarify for me? I though weight and tension would be working in the same direction?
I'm getting really discouraged because even going over physics every day doesn't seem to be helping me... argh.