11th Class Physics Motion in a Straight Line / सरल रेखा में गति Question Bank Motion In A Plane Conceptual Problems

  • question_answer
    Is \[|\vec{a}-\vec{b}|\] greater than or less than \[|\vec{a}|+|\vec{b}|\]?

    Answer:

                    \[|\vec{a}-\vec{b}{{|}^{2}}-{{(|\vec{a}|+|\vec{b}|)}^{2}}\] \[=|\vec{a}{{|}^{2}}+|\vec{b}{{|}^{2}}-2|\vec{a}||\vec{b}|\cos \theta -|\vec{a}{{|}^{2}}\] \[-|\vec{b}{{|}^{2}}-2\] \[|\vec{a}||\vec{b}|\] \[=-4|\vec{a}\text{ }\!\!|\!\!\text{   }\!\!|\!\!\text{ }\vec{b}|{{\cos }^{2}}\frac{\theta }{2}\]= a negative quantity Hence \[|\vec{a}-\vec{b}|\le |\vec{a}|+|\vec{b}|\].


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