Question

A 10 kW drilling machine is used to drill a brore in a small aluminium block of mass 8 kg. Find the rise in temperature of the block in 2.5 minutes, assuming 50% power is used upin heating the machine itself or lost to the surroundings.

(Specific heat of aluminium $= 091Jg^{- 1o}C^{- 1}$)

• A. 100 °C
• B. 103°C
• C. 150 °C
• D. 155 °C

Answer 1

Answer: (B)

103°C

Answer 2

Here, P = 10 kW $= 10^{4}W,$ m = 8 kg

Time , $t = 2.5$minute$= 2.5 \times 60 = 150s$

Specific heat, $s = 0.9Jg^{- 1}C^{- 1}$

Total energy $= P \times t = 10^{4} \times 150 = 15 \times 10^{5}J$

As 50% of energy is lost.

$\therefore$Energy available,

$\Delta Q = \frac{1}{2} \times 15 \times 10^{5} = 7.5 \times 10^{5}J$

As $\Delta Q = ms\Delta T$

$\Delta T = \frac{\Delta Q}{ms} = \frac{7.5 \times 10^{5}}{8 \times 10^{3} \times 0.91} = 103{^\circ}C$