Question Number 42357 by preet last updated on 24/Aug/18
Answered by tanmay.chaudhury50@gmail.com last updated on 24/Aug/18
$$\overset{\rightarrow} {{v}}=\frac{{d}\overset{\rightarrow} {{r}}}{{dt}}=\frac{{d}}{{dt}}\left(\mathrm{3}{ti}−{t}^{\mathrm{2}} {j}+\mathrm{4}{k}\right) \\ $$$$\overset{\rightarrow} {{v}}=\mathrm{3}{i}−\mathrm{2}{tj}+\mathrm{0}.{k} \\ $$$$\left(\overset{\rightarrow} {{v}}\right)_{{t}=\mathrm{5}{sec}} =\mathrm{3}{i}−\mathrm{10}{j}+\mathrm{0}.{k} \\ $$$${so}\:\mid\left(\overset{\rightarrow} {{v}}\right)_{{t}=\mathrm{5}{sec}} \mid=\sqrt{\mathrm{3}^{\mathrm{2}} +\left(−\mathrm{10}\right)^{\mathrm{2}} +\mathrm{0}^{\mathrm{2}} }\:=\sqrt{\mathrm{109}}\:\:{meter}/{sec} \\ $$