# Question 2983d

Mar 26, 2017

The ball weighs $80 \textcolor{w h i t e}{\text{." "kg}}$

#### Explanation:

Kinetic energy is found by the formula:

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

We know that $K E = 1000 \textcolor{w h i t e}{\text{.}} J$, and $v = 5 \textcolor{w h i t e}{\text{." "m/s}}$. Let's call the mass $M$ to avoid confusion between the mass variable and the symbol for meters.
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Now, let's plug in everything we know and solve for $M$.

1000 color(white)".""J" = 1/2 M * (5 color(white)"." "m/s")^2#

$1000 {\textcolor{w h i t e}{\text{." J = 1/2 M * 25 color(white)"." "m"^2"/s}}}^{2}$

$40 \textcolor{w h i t e}{\text{." "kg}} = \frac{1}{2} M$

$80 \textcolor{w h i t e}{\text{." "kg}} = M$