Question

$1kg$mass has $K.E.$ of $1J,$ when its speed is:

• A. $0.45m{s}^{-1}$
• B. $1m{s}^{-1}$
• C. $1.4m{s}^{-1}$
• D. $4.4m{s}^{-1}$

Answer 1

The correct option is C

$1.4m{s}^{-1}$

Step 1. Given data,

$$\begin{gathered} mass=1kg \\ K.E.=1J \end{gathered}$$

Step 2. Finding the value of $v$

We have $K.E=\frac{1}{2}m{v}^2$

$$\begin{gathered} 1=\frac{1}{2}\times 1\times v^2 \\ {v}^2=2 \\ v=\sqrt{2} \\ v=1.4m{s}^{-1} \end{gathered}$$

Thus, $1kg$mass has $K.E.$ of $1J,$ when its speed is $1.4m{s}^{-1}$. Hence, option ‘c’ is correct.