BMS1031 - Medical Biophysics question?

[alondouek]

As someone who has not done physics before, I'm a little bit stumped with a question:

"A pressure difference of 100 Pa results in a flow rate of 3 ml/s of water through a particular pipe.
If the pressure was increased to 800 Pa and the length halved, what would be the flow rate in ml/s?"

Probably really simple, but I'm just not getting it. I feel like I need to apply Poiseuille's Law, but there doesn't seem to be enough data for that?

Aargh.

[aznxD]

Firstly, the pressure difference increases by a factor of 8, hence flow rate increases by a factor of 8. ie. 24ml/s
Then the length is halved, so flow rate is doubled, so the final flow rate is 48ml/s

[alondouek]

Thank you so much!

[alondouek]

Another one that I have no idea how to work out:

"One cc of blood is moving in an artery and as it travels through a distance of 0.12 m it experiences a drag force F = 0.004 newton (in the direction opposing the blood's motion).
By how much does the blood's kinetic energy decrease in this distance, in joule?"

Edit: As the question asks for the answer in joules, is it simply Force x Distance?

[aznxD]

As the blood experiences the drag force, it's kinetic energy will decrease, as its velocity decreases. This decrease in kinetic energy is the change in kinetic energy which is defined as the work done. So yes, work = force x distance

[alondouek]

Thanks man, you're the best.

Another one if possible haha:

"A human is typically able to do physical work steadily at a rate of 150 to 500 watt (for 15-30 minutes) depending on level of fitness and which muscles are being used.

Assume for a particular person that the power needed for jogging on a treadmill is 200 watt when the resistive force (load) is set at 50 newton.

How far, in meter, can this person travel on the treadmill in 100 seconds?
Hint: consider the energy output for 100 second and its relation to the work done against the resistive force.

[aznxD]

Haha

Power = Change in energy / time
So Change in Energy =  P x t
Therefore change in energy = 200 x 100 = 20000 J
Work = change in energy = 20000 = f x d
d = 20000/f = 20000/50 = 400m

[alondouek]

I'm loving how I'm actually understanding this 

Last question, promise 

"Before an enthusiastic hiker climbs a mountain, 6 energy bars are consumed, each bar providing 200 kJ of chemical energy. The hiker's mass is 70 kg.
Only 20% of this food energy consumed is converted into useful physical work (output) when climbing. How high, in meter, can this hiker climb, using this energy."

I took 200 kJ x 6 = 1200 kJ,
then 1200 x 0.2 = 240 kJ
Then F=mg=70 x 9.8 = 686
Then, as D= W/F, (240/686) x 1000 = 349.9 m (but I'm probably entirely off)?

[aznxD]

The answer looks right to me
I did it another way using the formula for gravitational potential energy, as chemical energy is converted to kinetic energy which is in turn converted to gravitational potential energy as he is climbing the mountain.
PE = mgh = 240 kJ
h = (240E3)/(70 x 9.8 ) = 349.9m

[alondouek]

You are easily my favourite person right now 

[BigAl]

medical biophysics question? We're doing similar things in fluid dynamics in aerospace engineering.

[alondouek]

medical biophysics question? We're doing similar things in fluid dynamics in aerospace engineering.

Woah, really? That's pretty cool, but I guess there would be some theoretical overlap. Though, most of our stuff for fluid is generally in the context of the cardiovascular system, etc - I'd guess that the Aerospace Engineering theory would be more broad.

I really like this unit, but with no prior physics experience it's freaking difficult. Thank god for Khan Academy haha

[alondouek]

Quick question regarding elastance and compliance:

Preamble: Consider a pre-term baby with respiratory distress syndrome who is being ventilated by a positive pressure mechanical ventilator. The ventilator pushes air through the tube into the trachea intermittently with a frequency and pressure chosen by the physician (the ventilator can deliver each breath either at a fixed volume or a fixed inspiratory pressure). This baby weighs 2kg and the ventilator is set to deliver a peak inspiratory pressure (PIP) of 24cmH₂O. The tidal volume is 8ml.

"If the ventilator controls were changed to deliver a tidal volume of 25ml, what would you expect the PIP to be?"

The answer is given as 27cmH₂O. I've tried to manipulate the equations for elastance and compliance to get this answer but I can't seem to do so.

Help?

Elastance =

Compliance =

As far as I can tell, PIP is and tidal volume is