S.33 3-8

a)
$120\frac{km}{h}:3{,}6=33{,}3333....\approx33{,}333\frac{m}{s}$

$E_k=\frac{1}{2}mv^2=\frac{1}{2}\cdot1300kg\cdot\left(33{,}333\frac{m}{s}\right)^2=722207{,}7779\approx720000J=720kJ$
b)

$50\frac{km}{h}:3{,}6=13{,}8888\approx13{,}889\frac{m}{s}$

$40\frac{km}{h}:3{,}6=11{,}1111\approx11{,}111\frac{m}{s}$

$E_k=\frac{1}{2}mv^2=\frac{1}{2}\cdot1300kg\cdot\left(13{,}889\frac{m}{s}\right)^2=125387{,}8087J$

$E_k=\frac{1}{2}mv^2=\frac{1}{2}\cdot1300kg\cdot\left(11{,}111\frac{m}{s}\right)^2=80245{,}30865J$

$\frac{125387{,}8087J-80245{,}30865J}{125387{,}8087J}=0{,}36002...\approx0{,}36=36\%$
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