First slide

Thermal expansion

Question

When a metal sphere is heated, its volume increases by 50c.c and its surface area increases by 25cm². Its initial radius is

Easy

A

1.2cm
B

1cm
C

4cm
D

3cm

Solution

$\begin{array}{l} ΔA = AβΔt = 25 \\ ΔV = VγΔt = 50 \\ \frac{4 {πr}^{2} 2 α}{\frac{4}{3} {πr}^{3} 3 α} = \frac{1}{2} \\ r = 4 cm \end{array}$

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