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Help with unbalanced force

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  • #1
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Can you check if my answers are correct?

Suppose that the mass of the elevator and passengers were 1500 kg, and the frictional force (wheels on tracks) was 9000 N.

1. Draw a force diagram for the elevator.
Force of friction pointed up and force of gravity pointed down


2. Determine the acceleration of the elevator.
would it be -3.8 m/s^2 or 3.8 m/s^2?


3. Suppose that a 50.0 kg woman were standing on a bathroom scale in this elevator car. What would the scale read?

300 N


4. Determine how long it would take for the elevator car (starting from rest) to drop 30 floors (assume each floor is 3.0 m).

6.88 s

thanks!
 

Answers and Replies

  • #2
PeterO
Homework Helper
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Can you check if my answers are correct?

Suppose that the mass of the elevator and passengers were 1500 kg, and the frictional force (wheels on tracks) was 9000 N.

1. Draw a force diagram for the elevator.
Force of friction pointed up and force of gravity pointed down


2. Determine the acceleration of the elevator.
would it be -3.8 m/s^2 or 3.8 m/s^2?


3. Suppose that a 50.0 kg woman were standing on a bathroom scale in this elevator car. What would the scale read?

300 N


4. Determine how long it would take for the elevator car (starting from rest) to drop 30 floors (assume each floor is 3.0 m).

6.88 s

thanks!
All look OK.

Re the -3.8 or +3.8.

The acceleration is definitely down. Have you defined up or down as positive? [actually you don't need to define it, just say the acceleration is 3.8 ms-2 Down.
 

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