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I'm having an issue with two similar questions

 

1. A particle with uniform acceleration of 4ms-2 and covers 38 m over its fifth second of motion. Using its avarage velocity in this time period find the initial velocity.

 

2. A body moves with uniform acceleration. It travles 8.5m in the eight second and 7.5 m during the thirteenth second of it's motion. Using the average velocity from this time, find the initial velocity and acceleration.

 

Acceleration over this time using v=u+at v = 7.5 u = 8.5 t = 5

a = -0.2

Guest Nov 16, 2018
 #1
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1.OK.....what is the average velocity?

   It covered  38 m     in  0.2 sec

       Uh-ohh....your question is unclear in its  wording

           in second # 5  did i cover 38 m   or did it cover 38 m in   1/5 sec ????

    I will go with the former (though that is not what I initially thought)

 

vf = vo +  at       =   38 = vo +  (4)(5)

                                    38 = vo +  (20)

                                     18m/s = vo

 

2. vf = vo + at         =     7.5 = 8.5  + a(5)

                                      -1 = a 5

                                       - .2 = a      OK so we know the accel is negative 0.2  (it is DEccelerating....slowing down)

  vf = vo + at

  8.5 = vo + (-0.2)(8)

  8.5  = vo - 1.6

10.1 m/s = vo    

  (ALWAYS remember the UNITS)

ElectricPavlov  Nov 17, 2018
edited by ElectricPavlov  Nov 17, 2018

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