Question

(1) When 0.2kg of brass at 100°C is dropped into 0.5kg of water at 20°C, calculate the specific heat of brass.
(2) A 10kW drilling machine is used to drill in a small aluminium block of mass 8kg. How much is the rise in temperature of the block in 2.5minutes. Assuming 50% of power is lost to the surroundings. Specific heat of aluminium= 0.91 J/g°C.
(3) The wavelength and frequency of sound wave in a certain medium is 40cm and 825Hz respectively, keeping the medium unchanged, if the wavelength is changed to 32cm, calculate the resulting frequency?

Answer 1

(1) Heat gained by water = 42000 J
Heat lost by brass = (20S)J
According to principle of cal
20S= 42000
S= 2100J/kg°C

(2) Power of the drilling machine, P = 10 kW = 10 × 103 W
Mass of the aluminum block, m = 8.0 kg = 8 × 103 g
Time for which the machine is used, t = 2.5 min = 2.5 × 60 = 150 s
Specific heat of aluminium, c = 0.91 J g–1 K–1
Rise in the temperature of the block after drilling = δT
Total energy of the drilling machine = Pt
= 10 × 103 × 150
= 1.5 × 106 J
It is given that only 50% of the power is useful.

Therefore, in 2.5 minutes of drilling, the rise in the temperature of the block is 103°C.

(3) 40cm= 825hz
Then 32cm= ?
32×825÷40=
660hz