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Force and Laws of Motion — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceForce and Laws of Motion4 Marks
Question
State and explain Newton’s second law of motion.
✓

Answer

According to Newton's second law of motion: The rate of change of momentum of a body is directly proportional to the applied force, and takes place in the direction in which the force acts.
Consider a body of mass m having initial velocity u. the initial momentum of this body will be mu. Suppose a force F acts on this body for time t causing the final velocity to be v. The final momentum of the body will be mv. Now the change in momentum is mv → mu and the time taken for this change is t. So according to Newton's second law of motion,
$\text{F}\propto\frac{\text{mv}-\text{mu}}{\text{t}}$
$\text{F}\propto\frac{\text{m}(\text{v}-\text{u})}{\text{t}}$
But $\frac{(\text{v}-\text{u})}{\text{t}}$ represents change in velocity with time i.e. ascceleration 'a'. So br replacing $\frac{(\text{v}-\text{u})}{\text{t}}$ with a in the above relation, we get
$\text{F}\propto\text{m}\times\text{a}$
Thus, the force acting on a body is directly proportional to the product of mass and acceleration produced in the body by the action of the force. Thus, Newton's second law gives the relationship between force and acceleration.

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