Question

A 10kW drilling machine is used to drill a bore in a small aluminium block of mass 8.0kg. How much is the rise in temperature of the block in 2.5 minutes, assuming 50% of power is used up in heating the machine itself or lost to the surroundings? Specific heat of aluminium = 0.19Jg^-1 K^-1.

Answer 1

Power, P = 10 kW

= 10 × 10³W

= 10⁴W

Mass, m = 8 kg; Time, t = 2.5min = 150s

Specific heat, c = 0.91Jg^-1K^-1

= 0.91 × 10³Jkg^-1K^-

Energy, Q = pt = 10⁴ × 150J = 1.5 × 10⁶J

It is given that 50% of energy is lost to the. surroundings. So, energy absorbed by the block is given by

Q = \(\frac{1}{2}\) × 1.5 × 10⁶J = 0.75 × 10⁶

But Q = mc∆T

∴ ∆T