.
(a) the average acceleration a = is the velocity change divided by the time
a = = = = 10 m/s^2.
(b) The average force, according to the Newton second law, is the product
of the acceleration by the mass
= m*a = 15 kg * 10 m/s^2 = 150 newtons.
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These are the basic knowledge on kinematic and dynamic.
These notions and formulas (laws) are fundamental basis of Physics, similar to as the multiplication table is the basis of Arithmetic.
If you want references to good textbooks, here they are
Taffel - Physics: its methods and meaning (for 6-8 grade students).
Giancoli - Physics. Principles with applications (for 9-11 grade students).