Question

The kinetic energy of an electron is $4.55\times {10}^{-25}J$.The mass of electron is $9.1x{10}^{-31}\mathrm{kg}$ .The velocity of the electron is .

• A. ${10}^2{\mathrm{ms}}^{-1}$
• B. ${10}^3{\mathrm{ms}}^{-1}$
• C. $10{\mathrm{ms}}^{-1}$

Answer 1

The correct option is B ${10}^3{\mathrm{ms}}^{-1}$

Calculation of the velocity of energy:
Kinetic energy $=\frac{1}{2}m{v}^2=4.55\times {10}^{-25}J$

$=4.55\times {10}^{-25}kg{m}^2{s}^{-2}$

Or $v^2=\frac{2\times KE}{m}=\frac{2\times (4.55\times {10}^{-25}kg{m}^2{s}^{-2})}{(9.1\times {10}^{-31}kg)}$

$={10}^6{m}^2{s}^{-2}$

Or velocity $\left(v\right)=({10}^6{m}^2{s}^{-2}{)}^{\frac{1}{2}}={10}^{3}m{s}^{-1}$