Consider an acrylic sheet of thickness L = 5 mm that is used to coat a hot, isothermal metal substrate at Th = 300°C. The proper
ties of the acrylic are rho = 1990 kg/m3, c = 1470 J/kg · K, and k = 0.21 W/m · K. Neglecting the thermal contact resistance between the acrylic and the metal substrate, determine how long it will take for the insulated back side of the acrylic to reach its softening temperature, Tsoft = 90°C. The initial acrylic temperature is Ti = 20°C.
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Answer:
Explanation:
Light rays coming from moon is blocked by the pencil
so as per figure we know that angle subtended by pencil and angle subtended by moon must be same
so we have
so we have
so we have
