Medi11002 Physics For Health Sciences- Assessment Answers

Part 2

1. For each of the statements below, indicate whether the statement is true or false and explain your reasoning.
a. As a medical supply trolley is wheeled around a curved pathway, its velocity and acceleration remains unchanged.
b. When an elastic band is stretched around a patient’s arm to act as a tourniquet, there is no work done and the band has no stored energy.

2. A student healthcare professional has been asked to move a box of mass 12 kg onto a shelf that is at a height 0.3 m above the ground level and 5.5 m from where the box was originally kept. The student is holding the box and moving with the box in a straight line at a steady speed of 0.15 m/s. As the student approaches the shelf, he notices another student is opening the door adjacent to the shelf area. If the student is able to apply sufficient force to stop in 2. s, will the student avoid a collision if the opening door is 1.0 m ahead of the box? (Assume that the student is applying the same magnitude of force throughout that time).

3. Whist waiting for your next lecture session, you purchase a single-serve soft drink in a standard plastic bottle with screw-on lid. You open the lid to take a drink, and notice fluid flowing from a small hole in the bottom of the bottle. You put the lid back on the bottle to return it to the store as defective. However, once you put the lid back on, the flow from the hole stops!

i. Differentiate between the properties of the soft drink and the plastic bottle.

ii. Explain why flow did not start until the lid was off the bottle.

Answers

Part 1

Velocity - is the distance travelled per unit time

Acceleration- rate of change of velocity per unit time factor

Work - an activity which is done using physical or mental capacity

Force - interaction which when unopposed it changes the motion of a body

Adhesion - attraction between similar particles or molecules

Cohesion- attraction between different molecules

Atmospheric pressure- pressure which results from the weight of atmosphere.

Part 2

1a. False, this is because the both velocity and acceleration are able to depend on the direction of movement, which is changing in this case, and therefore they are able to change.   

b. True there is no work done since the distance moved is zero. Work is only done when there is a distance movement. Nevertheless, the band has potential energy which is stored upon when it is stretched.

2. Mass = 12kg

Height =0.3m

Distance = 5.5 m

Speed = 0.15m/s

Force applied in moving the box

F = ma

Time required to move 5.5 m at 0.15 second is given as

T =d/s

= 5.5/0.15 = 36.667 second

The acceleration = speed / time

= 0.15/ 36. 667 = 0.00409 m/s²

Force = mass x acceleration

= 12 x 0.00409 = 0.049 N

Time needed to stop on spotting the opening door at 1 m

Since the force and mass are constant, the student will require the same acceleration to stop when he sees the door

Force = 0.049N

Acceleration = f /  m = 0.049/12 = 0.00409 m/s²

The velocity which the student need to move in order to avoid knocking the door = ½ = 0.5 m/s

Time required to stop when carrying the box =  velocity /acceleration

=   t =v/ a

time = Velocity /acceleration

= 0.5/ 0.00409 m/s² 

= 122.25 sec

This means that 2 sec will so less to prevent the collision.

3i. The plastic and the soft drink have different types of molecules and therefore their cohesive forces are less than the adhesive forces between the similar molecules. This means that the drink will be able to flow out when it gets an opportunity and fail to attract the plastic molecules (Field trip videos inc., and AIMS MEDIA. (1992). In addition, the difference in molecule types is able to enhance the flowing out of the soft drink. The attraction of the similar molecules between the molecules is able to enhance the detachment whenever the bottle is open. In addition, the liquid particles are closed packed while the solids ones are tightly parked. In addition, liquids particles are able to jigle and slide against each other leading to the flow but solid particles are tightly parked and do not move around.

ii. Opening the lid is able to exert more pressure on the top of the liquid and therefore leading to the flow of the liquid out of the bottle. The atmospheric pressure is able to add to the pressure of the liquid and therefore lead to the flow (Rodgers, Evans, & Leigh Marine Laboratory, 1983).On the same case, when the bottle is closed, the atmospheric pressure is withdrawn and therefore leads to the stoppage of the flow. The atmospheric pressure is constant and whenever allowed to act, it creates the difference in pressure between the top part and the bottom part of the bottles and therefore lead to out flow of the soft drink. The atmospheric pressure is able to add to the pressure which is created by the drink itself. When the bottle is closed, the pressure at the bottom of the bottle is the same as the pressure at the top of bottle (Rodgers, Evans, & Leigh Marine Laboratory, 1983). This means the soft drink will not be able to flow out without the additional pressure on top.

References

Field trip videos inc., and AIMS MEDIA. (1992). Temperature, pressure and humidity. CharyFieldh, Calif: AIMS Media.

Rodgers, D, W., Evans J, H., & Leigh Marine Laboratory. (1983). Atmospheric pressure. Leigh, N. Z. University of Auckland, Marine Laboratory. .