$\mathbf{PE}\mathbf{}\mathbf{=}\mathbf{}\mathbf{m}\mathbf{\times}\mathbf{g}\mathbf{\times}\mathbf{h}\phantom{\rule{0ex}{0ex}}\mathbf{PE}\mathbf{}\mathbf{=}\mathbf{(}\mathbf{2}\mathbf{.}\mathbf{70}\mathbf{}\frac{\overline{)\mathbf{g}}}{\overline{){\mathbf{cm}}^{\mathbf{3}}}}\mathbf{\times}\mathbf{196}\mathbf{}\overline{){\mathbf{cm}}^{\mathbf{3}}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{kg}}{{\mathbf{10}}^{\mathbf{3}}\mathbf{}\overline{)\mathbf{g}}}\mathbf{)}\mathbf{(}\mathbf{9}\mathbf{.}\mathbf{8}\mathbf{}\frac{\mathbf{m}}{{\mathbf{s}}^{\mathbf{2}}}\mathbf{)}\mathbf{(}\mathbf{2}\mathbf{.}\mathbf{1}\mathbf{}\mathbf{m}\mathbf{)}$

**PE = 10.89 J**

Consider the two spheres shown here, one made of silver and the other of aluminum. The spheres are dropped from a height of 2.1 m.

What is the kinetic energy of the silver sphere at the moment it hits the ground? (Assume that energy is conserved during the fall and that 100% of the sphere’s initial potential energy is converted to kinetic energy by the time impact occurs.)

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