Question 1166379
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<pre>

(a)  the average acceleration  a = {{{a[average]}}}  is the velocity change divided by the time


         a = {{{a[average]}}} = {{{(20-0)/2}}} = {{{20/2}}} = 10 m/s^2.



(b)  The average force, according to the Newton second law, is the product 

     of the acceleration by the mass


        {{{F[average]}}} = m*a = 15 kg * 10 m/s^2 = 150 newtons.
</pre>

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These are the basic knowledge on kinematic and dynamic.


These notions and formulas &nbsp;(laws) &nbsp;are fundamental basis of &nbsp;Physics, similar to as the multiplication table is the basis of Arithmetic.


If you want references to good textbooks, &nbsp;here they are



    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Taffel - Physics: its methods and meaning (for 6-8 grade students).


    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Giancoli - Physics. Principles with applications (for 9-11 grade students).