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Question:

yrcah
yrcah
Student
High School - 9th Grade

How long will the acceleration of 10 m/2 take place if the bus will run 25m/s and will change to 15 m/s?

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Posted by yrcah on Tuesday October 6, 2009 at 5:04 AM and tagged with motion, physics, science, word problems.

Answers:

  1. neela
    neela Teacher
    Graduate School

    eNotes Editor

    The acceleration of 10 m/s^2 should act in opposing direction of the velocity of the bus in order that the velocity (speed) of 25m/s comes down to 15m/s.

    We know that acceleration is the rate of change of velocity.

    Therefore, acceleration =( Final velocity -initial velocity )/time

    Therefore -10m/s^2 = [(15-25)m/s]/t

    t= (15-25)/(-10 )secs

    =10/10

    =1 secs.

    Therefore the acceleration of 10 m/s^2 should act for 1 seconds in a direction opposite to the velocity of the bus.

     

     

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    Posted by neela on Tuesday October 6, 2009 at 5:21 AM

  2. krishna-agrawala
    krishna-agrawala Teacher
    Graduate School

    eNotes Editor

    Given acceleration a = -10 m/s^2, initial velocity u = 25 m/s, and

    final velocity v = 15 m/s.

    Please note that accelaration is taken as negative because te speed decreases.

    Then time taken for change in velocity t = (v - u)/a

    = (15 - 25)/(-10) = 1

    Answer: The acceleration should take place for 1 s.

     

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    Posted by krishna-agrawala on Tuesday October 6, 2009 at 6:13 AM

  3. mamta88
    mamta88 Student
    Graduate School

    initial velocity=u=25m/s;final velocity=v=15m/s

    acceleration=a=10m/s^2

    a=(v-u)/t

    =>t=-a/(v-u)

           =-10/(15-25)

           = -10/-10

           = 1 sec

    Because the velocity is decreased,hence acceleration is negative.

     

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    Posted by mamta88 on Thursday November 5, 2009 at 7:45 AM

  4. mamta88
    mamta88 Student
    Graduate School

    initial velocity=u=25m/s;final velocity=v=15m/s

    acceleration=a=10m/s^2

    a=(v-u)/t

    =>t=-a/(v-u)

           =-10/(15-25)

           = -10/-10

           = 1 sec

    Because the velocity is decreased,hence acceleration is negative.

     

     

    The first answer is incorrect as the final velocity is given as 15m/s instead of 10 m/s..

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    Posted by mamta88 on Thursday November 5, 2009 at 7:47 AM

  5. spralph
    spralph

    1.5 sec

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    Posted by spralph on Tuesday November 10, 2009 at 4:07 AM

  6. gfoote3064
    gfoote3064 Teacher
    High School - 9th Grade

    eNotes Editor

    The velocity changes from 25 m/sec to 15 m/sec. This represents a change of 10 m/sec. An acceleration of 10m/sec/sec implies that there will be a change of 10 m/sec for every second the acceleration acts. So change in velocity  = acceleration times time. So, in this case, t = 1.0 seconds.

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    Posted by gfoote3064 on Sunday November 22, 2009 at 6:22 PM