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    ineken's Avatar
    ineken Posts: 4, Reputation: 1
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    #1

    Oct 4, 2011, 10:29 AM
    Help with physics homework
    A 65 kg man stands on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.2 m/s in 0.89 s. It travels with this constant speed for 5.0 s, undergoes a uniform negative acceleration for 1.2 s, and comes to rest. What does the spring scale register in each of the following time intervals?
    (a) before the elevator starts to move
    N
    (b) during the first 0.89 s
    N
    (c) while the elevator is traveling at constant speed
    N
    (d) during the negative acceleration
    N
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Oct 4, 2011, 12:28 PM
    In each case you get your answer is found using F = ma, where 'a' (acceleration) has two components: the acceleration due to gravity - called 'g' - plus the acceleration of the elevator - call it a_e. Hence the force with which the man's body pressses down on the scale is equal to F = m(g+a_e)

    In question (a) the acceleration due to the elevator is 0. So what do you get for F?

    In question (b) you need to add the acceleration of the elevator a_e, which you can determine based on the data you've been given. You add a_e because the acceleration is upward, so it takes a greater force to be applied between the scale and the man to accelerate him upward.

    Can you finish it out from here?
    ineken's Avatar
    ineken Posts: 4, Reputation: 1
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    #3

    Oct 4, 2011, 12:59 PM
    Yes I got it thank you

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