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Q.State Newton's second law of motion. Hence derive the equation of motion F = ma from it.

Andhra Pradesh BieapBIEAP Intermediate Board (1st Year) 2019Subjective· 4mImportance★★★★★
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Newton's second law says force equals the rate of change of momentum; for a body of constant mass, this reduces directly to F=maF = ma.

Statement of Newton's second law

The rate of change of linear momentum of a body is directly proportional to the applied external force, and the change in momentum takes place in the direction of the applied force.

Derivation of F=maF = ma

Let a body of mass mm have momentum p⃗=mv⃗\vec{p} = m\vec{v}, where v⃗\vec{v} is its velocity.

By Newton's second law:

F⃗∝dp⃗dt\vec{F} \propto \frac{d\vec{p}}{dt}

F⃗=k dp⃗dt\vec{F} = k\,\frac{d\vec{p}}{dt}

where kk is a constant of proportionality.

Substituting p⃗=mv⃗\vec{p} = m\vec{v}:

F⃗=k d(mv⃗)dt\vec{F} = k\,\frac{d(m\vec{v})}{dt}

If the mass mm of the body remains constant with time (as is true for ordinary mechanics, non-relativistic and no mass loss/gain): …

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