Physics Assessmrnt
Question 1(10 marks)
Comment the following statements
(a) The volume coefficient of thermal expansion of water is negative for temperatures in the range 0 to 4 °C.
(b) The triple point of water, 0.01 °C, and 611.73 Pa, is one of the primary fixed points on the Kelvin absolute temperature scale.
(c) The volume coefficient for the thermal expansion of a solid is twice the linear coefficient for thermal expansion.
(d) A temperature of 26.85 °C is the same as 300 K.
(e) The surface temperature of the sun (3142 °C) is the highest temperature found in nature.
Question 2 (10 marks)
A sample of an unknown gas (gas A) has a volume of 3.2 m3 at a temperature of 10 °C. Another sample of an unknown gas (gas B) has a volume of 4.5 m3 at a temperature of 250 °C. Assuming that both gases obey Charles’ law at all temperatures and are at the same pressure,
(a) Could gas A and gas B be samples of the same gas at different temperatures?
(b) What is the volume of gas A at the following temperatures: -50 °C, 0 °C, 50 °C, 100 °C ?
Question 3 (10 marks)
The core temperature of an athlete is 37 °C and his surface area is 1.8m2. The thermal conductivity of his surface tissue, which is 6mm thick on average, is 0.18Wm−1 K−1. If heat is transferred from his core to his skin at a rate of 270W, what is the average temperature of his skin surface?
Question 4 (15 marks)
A cyclist does 2 MJ of mechanical work over the course of a day. His work efficiency is 20% and the metabolic energy of the food consumed during the day is 8MJ.
(a) What is the net metabolic energy used during the day?
(b) How much heat does the cyclist transfer to his surroundings during the day?
(c) How much extra food will the cyclist need to consume at the end of the day in order not to loose weight?
Question 5 (9 marks)
In a chemical reaction, the two ends of a 2.45-m-long DNA molecule acquire charges of +e and –e , respectively. What is the force between the two ends of the molecule?
Comment the following statements
(a) The volume coefficient of thermal expansion of water is negative for temperatures in the range 0 to 4 °C.
(b) The triple point of water, 0.01 °C, and 611.73 Pa, is one of the primary fixed points on the Kelvin absolute temperature scale.
(c) The volume coefficient for the thermal expansion of a solid is twice the linear coefficient for thermal expansion.
(d) A temperature of 26.85 °C is the same as 300 K.
(e) The surface temperature of the sun (3142 °C) is the highest temperature found in nature.
Question 2 (10 marks)
A sample of an unknown gas (gas A) has a volume of 3.2 m3 at a temperature of 10 °C. Another sample of an unknown gas (gas B) has a volume of 4.5 m3 at a temperature of 250 °C. Assuming that both gases obey Charles’ law at all temperatures and are at the same pressure,
(a) Could gas A and gas B be samples of the same gas at different temperatures?
(b) What is the volume of gas A at the following temperatures: -50 °C, 0 °C, 50 °C, 100 °C ?
Question 3 (10 marks)
The core temperature of an athlete is 37 °C and his surface area is 1.8m2. The thermal conductivity of his surface tissue, which is 6mm thick on average, is 0.18Wm−1 K−1. If heat is transferred from his core to his skin at a rate of 270W, what is the average temperature of his skin surface?
Question 4 (15 marks)
A cyclist does 2 MJ of mechanical work over the course of a day. His work efficiency is 20% and the metabolic energy of the food consumed during the day is 8MJ.
(a) What is the net metabolic energy used during the day?
(b) How much heat does the cyclist transfer to his surroundings during the day?
(c) How much extra food will the cyclist need to consume at the end of the day in order not to loose weight?
Question 5 (9 marks)
In a chemical reaction, the two ends of a 2.45-m-long DNA molecule acquire charges of +e and –e , respectively. What is the force between the two ends of the molecule?