Question 15 Marks
Two toy$-$cars $A$ and $B$ of masses $200 g$ and $500 g$ respectively are moving with the same speed. Which of the two has greater kinetic energy?
Answer
View full question & answer→$\text{CAR}\ A$
$ \text { mas }=200 g$
$=\frac{200}{1000}=\frac{1}{5} \ kg$
$=0.2 \ kg$
$\text { K.E. }=\frac{1}{2} M V^2$
$ \text { K.E. }=\frac{1}{2} \times 0.2 \times V^2$
$=0.1 v^2 $
$\text{CAR}\ B$
$\text { mass }=500 g $
$=\frac{500}{1000}=0.5 \ kg $
$\therefore$ speed of both cars is same
$ \text { K.E. of } B =\frac{1}{2} \times 0.5 \times V^2$
$ =0.25 v^2$
$0.25 v^2$ is greater than $0.1\ v^{2}$
$\therefore \text{K.E.}$ of car $B$ is greater.
Or
Since speed of both cars is same
$\therefore$ The speed of car having greater mass $($i.e. of car $B)$, the $\text{K.E}$. is greater
$\therefore$ Kinetic energy of car $B$ having greater mass is greater.
$ \text { mas }=200 g$
$=\frac{200}{1000}=\frac{1}{5} \ kg$
$=0.2 \ kg$
$\text { K.E. }=\frac{1}{2} M V^2$
$ \text { K.E. }=\frac{1}{2} \times 0.2 \times V^2$
$=0.1 v^2 $
$\text{CAR}\ B$
$\text { mass }=500 g $
$=\frac{500}{1000}=0.5 \ kg $
$\therefore$ speed of both cars is same
$ \text { K.E. of } B =\frac{1}{2} \times 0.5 \times V^2$
$ =0.25 v^2$
$0.25 v^2$ is greater than $0.1\ v^{2}$
$\therefore \text{K.E.}$ of car $B$ is greater.
Or
Since speed of both cars is same
$\therefore$ The speed of car having greater mass $($i.e. of car $B)$, the $\text{K.E}$. is greater
$\therefore$ Kinetic energy of car $B$ having greater mass is greater.