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Two solid spheres made of the same metal have weights 5920 g and 740 g, respectively. Determine the radius of the larger sphere, if the diameter of the smaller one is 5 cm.

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Answer : 5\; cm

Density (D) of an object is mass (m) per unit volume (v).

D=\frac{m}{v}

So mass is directly proportional to volume for same metal (as density remains same)

For Solid 1

Let Mass = M_{1}

Volume = V_{1}

For  solid 2

Mass = M_{2}

Volume = V_{2}

Now, \frac{M_{1}}{M_{2}}=\frac{V_{1}}{V_{2}}

In the question, the objects are spheres

Volume of sphere =\frac{4}{3}\pi R^{3}           (where R is radius)

So, volume is directly proportional to R^{3}

Hence, \frac{M_{1}}{M_{2}}=\frac{V_{1}}{V_{2}}=\frac{R_{1}^{3}}{R_{2}^{3}}

Putting the given values \left ( 5920\; g \; and\; 740\; g \right )

\Rightarrow \frac{5920}{740}=\frac{R_{1}^{3}}{R_{2}^{3}}

\Rightarrow \frac{R_{1}^{3}}{R_{2}^{3}}=8

\Rightarrow \frac{R_{1}}{R_{2}}=\sqrt[3]{8}

\Rightarrow \frac{R_{1}}{R_{2}}=2

So, R_{1}=R_{2}\times 2

Diameter of the smaller one is 5 cm

So, R_{2}=\frac{5}{2}=2.5\; cm

R_{1}=2.5 \times 2

Hence, R_{1}=5\; cm

Therefore radius of larger sphere is 5 cm.

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