Derive third law of motion from first law
Answers
Answer:
To derive 1st law from 2nd law f = ma is easy. Just put F = 0, no force is applied to the body in question. This brings about ma =0. Since m , mass is not 0 obviously, this forces a =0. No acceleration means no change in velocity. If the initial velocity is 0, it would remain 0, this is inertia of rest. If the initial velocity is u, v = u+at = 0 again since a=O.
Now suppose two bodies collide . Each exerts a force on the other . Let them be F1 and F2 respectively. If the two bodies constitute a system, there is no external forces on the system. Both the mutual forces become internal forces on the system. So their common centre of mass shall be in inertia of rest or motion. Thus F1+F2=0, i.e., F1=-F2. The mutual forces are equal and opposite. This is Newton's third law.
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Explanation:
Newton's first law states that a body stays at rest if it is at rest and moves with a constant velocity unit if a net force is applied on it. Newton's second law states that the net force applied on the body is equal to the rate of change in its momentum.
F = ma
F = maor F = m(v-u) / t
F = maor F = m(v-u) / tor Ft = mv - mu
That is, when F = 0, v = u for whatever time, t is taken. This means that the object will continue moving with uniform velocity, u throughout the time, t. If u is zero than v will also be zero, i.e., object will remain at rest.