Assignment 1c Solutions

Name: ______________________________Student no: _____________ Group:_______________ CC2404 Applied Physics and Instrumentation in Health Care Assignment 1C Duration: 30 min 1. When a rock falls freely, which of the following energy is decreasing? (Assuming no air friction). A. Potential energy B. Mechanical energy C. Kinetic energy Answer:___A_ (1 mark)

2. State two types of thermometer used for body temperature measurement, and suggest why they can be used for such a purpose. Mercury thermometer: the volume of mercury expands when the temperature increases and contract when the temperature decreases. Thermistor: the resistance of material changes when the temperature is varied. Thermocouple: voltage produced between two junctions when there is a temperature difference. Infrared theromoeter: wavelength and intensity of IR emitted by a person changes with temperature. (2 marks)

3. State two ways used by our bodies for producing cooling in order to control the body temperature. Increase in the flow rate of the blood to skin capillaries, sweating (2 marks)

4. Energy not used by human body for work is converted to fat. Each gram of fat can store 38.9 kJ of energy. How many grams of fat will you gain, if you eat 3500 kcal one day and do nothing but sit for 18.0 h and sleep for the rest of the day? (assume that the energy consumption is 1.2 kcal/min for sleeping, and 1.8 kcal/min for sitting, 1 kcal = 4.186 kJ). Energy consumed=1.8 kcal/min x18x60min + 1.2 kcal/min x 6 x 60 min=2376kcal Energy stored=3500-2376=1124 kcal=4705kJ Fat=4705/38.9=121 g (3 marks)

5. For every 50 J of electrical energy entering a light bulb, 3 J of useful light energy is produced. (a) Calculate the efficiency of the light bulb. 3J/ 50 J = 6% (1 marks) (b) In which forms can the remaining energy be changed into? Give one example. Heat energy

(1 mark)

6. A fish has a mass of 50.0 kg in air and density of 860 kg/m3. Find the buoyant force (in N) exerts on the fish, when it is completely in the water (given the density of water is 1000 kg/m3, 1 kg=10 N). volume V = m/D = 50 kg /860 kgm-3 = 0.05814 m3 so buoyant force F = 0.05814 * 1000 * 10 = 582 N (3 marks)

Name: ______________________________Student no: _____________ Group:_______________