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$$
\begin{array}{l}{\text { Calculate the total kinetic energy, in } \mathrm{kJ}, \text { of an object whose mass is } 100 \mathrm{kg}} \\ {\text { and whose velocity is } 20 \mathrm{m} / \mathrm{s} \text { . }}\end{array}
$$

$$
m=100 k g
$$

$$
V=20 \mathrm{m/S}
$$

$$
\mathrm{kE}  \text { ?? }
$$

$$
K E=\frac{1}{2} m v^{2}
$$$$
=\frac{1}{2}(100)(20)^{2} *
$$$$
\left(\frac{1\frac{ KJ}{Kg}}{1000m^2/s^2}\right)
$$

$$
={20} \mathrm{k}_{\mathrm{J}}
$$

$$
\begin{array}{l}{\text { Calculate the total potential energy, in } \mathrm{kJ} \text { , of an object whose mass is } 20 \mathrm{kg}} \\ {\text { when it is located } 20 \mathrm{m} \text { below a datum level in a location where } g=9.5 \mathrm{m} / \mathrm{s} 2 .}\end{array}
$$

$$
m=2{0} k g
$$

$$
Z=20 \mathrm{m}
$$

$$
9=9.5
$$

$$
P E=m g z=20 * 9.5 *(-20) *\left(\frac{1\frac{KJ}{Kg}}{1000 \frac{m^ 2}{s^2}}\right)
$$

$$
=-3.8 \mathrm{K} \mathrm{J}
$$

$$
\begin{array}{l}{\text { A small electrical motor produces } 5 \mathrm{W} \text { of mechanical power. }} \\ {\text { What is this power in (a) } \mathrm{N}, \mathrm{m}, \text { and s units }} \\ {\text { and }(\mathrm{b}) \mathrm{kg}, \mathrm{m}, \text { and } \mathrm{s} \text { units? }} \\ {\text { Answers: (a) } 5 \mathrm{N}-\mathrm{m} / \mathrm{s},(\mathrm{E}>) 5 \mathrm{kg}-\mathrm{m} 2 / \mathrm{s} 3}\end{array}
$$

(a) $$
\dot{w}=5 w(\frac{1 j/s}{1w})(\frac{1N.m}{1J})=5 N.m/s
$$

(b) $$
\dot{w}=5 w (\frac{1J/S}{1W})(\frac{1 N.m}{1J})(\frac{1ks.m/s^2}{1N})
$$

$$
=5 \mathrm{kg} \cdot \mathrm{m}^{2} / \mathrm{s}^{3}
$$

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