Elevator pulled upward by cable - find tension

AI Thread Summary
The discussion focuses on calculating the tension in a cable pulling an elevator upward with a combined mass of 2000 kg. When a coin is dropped inside the cab, it accelerates downward at 8.00 m/s², indicating that the elevator is decelerating. The tension in the cable is derived from the net force equation, where the upward tension is slightly less than the weight of the cab and occupant due to the downward acceleration. The calculation confirms that the tension is 16,000 N, reflecting the elevator's slowing motion. Understanding the relationship between the coin's acceleration and the elevator's movement is key to solving the problem accurately.
shawpeez
Messages
16
Reaction score
0
here's the question,

An elevator cab is pulled upward by a cable. The cab and its single occupant have a combined mass of 2000kg. When that occupant drops a coin, its acceleration relative to the cab is 8.00m/s^2 downward. What is the tension in the cable?

could someone explane to me how to relate the accerleration of the coin downward to the acceleration of the cab being pulled up.
 
Physics news on Phys.org
IF the elevator is going up, and the apparent acceleration in the cab is less than 9.8 m/s/s, then the elevator is at that moment slowing down.

If an object is being pulled up at a constant velocity, then there is zero acceleration because forces are balanced (specifically, the tension in the cable balances the weight). Dropping the coin inside at this moment, the coin would display normal acceleration to the person inside the cab, no matter what speed the elevator was doing.

If the elevator is slowing down, then the upward tension in the cable must be slightly less than the total weight (thereby making net force NOT zero but slightly downward).

So what's the accelration of the cab, if gravitational acceleration "seems to be" 1.8 m/s/s less than normal?
 
My first instinct was that the upward acceleration of the cab was slowing down, this is what i did

Fnet= T - mg = ma
T - 2000(9.8) = 2000(-1.8)
T - 19600 = -3600
T= 19600 - 3600
T = 16000 N

Is this correct ?
 
You are correct. Follow that instinct (but don't say "the acceleration was slowing down," it's the speed that is slowing down.)
 
thanks for the help:smile:
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Back
Top