Ultrasound can be used to determine the properties of materials, and to find the shape of objects and the distance between them. (a) how do ultrasound systems determine the density of a material? what would make it difficult to "see" a marble hidden inside an air-filled hollow black box using ultrasound? explain using physics concepts. (2 marks) (b) a sound wave generated by an ultrasound "wand" reflects off a bone that is situated 3cm inside a water sample. water has an acoustic impedance of 1.48 mpa s / m and bone has an acoustic impedance of 7.75 mpa s / m. the output of the wand is perfectly matched with water (with gel) so that ultrasonic waves enter the medium without reflection and travel at 1 484 m/s. the amount of reflection off the boundary between two objects can be found with the following equation 2 z2 - z2 r2 \z, +z2. (i) how much of the ultrasound is reflected back to the receiver? (1.5 marks) (i) how long does it take for the sound to return to the wand after it is emitted?

Work out sian speed for the first 30 minutes of her journey. give your answer in km/h.

An insulated 40 ft^3 rigid tank contains air at 50 psia and 120°f. a valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 25 psia. the air temperature during this process is kept constant by an electric resistance heater placed in the tank. determine the electrical work done during this process.

1. the materials manager for a billiard ball maker must periodically place orders for resin, one of the raw materials used in producing billiard balls. she knows that manufacturing uses resin at a rate of 50 kilograms each day, and that it costs $.04 per day to carry a kilogram of resin in inventory. she also knows that the order costs for resin are $100 per order, and that the lead time for delivery is four (4) days.2. at what point should resin be reordered? a. 0 kilograms remainingb. 50 kilograms remainingc. 200 kilograms remainingd. 400 kilograms remaininge. 500 kilograms remaining3. if order size was 1,000 kilograms of resin, what would be the length of an order cycle? a. 0.05 daysb. 4 daysc. 16 daysd. 20 dayse. 50 days4. if the order size was 1,000 kilograms of resin, what would be the average inventory level? a. 50 kilogramsb. 200 kilogramsc. 500 kilogramsd. 800 kilogramse. 1,000 kilograms5. if the order size was 1,000 kilograms of resin, what would be the daily total inventory costs, excluding the cost of the resin? a. $5b. $10c. $20d. $25e. $40