Help, please? (physics).

Question

2. The human heart is a powerful and extremely reliable pump. Each day (24 hours) it

takes in and discharges about 7500 litres of blood and the heart must do work in

lifting this mass of blood as it circulates round the body.

(a) If each litre of blood has a mass 1.05 kg what is the total mass of blood taken in

and discharged by the heart in 24 hours

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(b) If the strength of gravity is 9.8 N/kg what is the lifting force in Newtons required to

lift this mass of blood?

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(c) The work done by a woman’s heart would equal the work done in lifting this weight

of blood through a distance equal to an average height of 1.63 m. Calculate the

work done in joules by the heart in 24 hours.

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(d) Calculate the power of the human heart in joules per second when working as

above.

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Answer 1

a)7875 kg

b)77175 N

c)125795.25 J

d)1.45 J/s

Answer 2

This question is a fair exercise and others have dealt with it as stated;however there is a nonsence about it since the circulation is a closed circuit so no pumping against gravity occurs, unless of course some poor wasname has literaly lost its head.Sorry to be a misery!

Answer 3

a) Mass of blood = total discharge*mass of a litre = 7500x 1.05 =7875kg

b) F=ma in this case a is acceleration due to gravity

F= 7500 x 9.8 = 73500N

c)Work done = mgh = 7500 x 9.8 x 1.63 = 125795.25 J = 125.8KJ

d) Power = Work/time

First we need to find total time in seconds:

3600 seconds in a hour, 24 hours in a day, total time = 24x 3600  =86400seconds.

Now we simply use the above equation, taking work from question c)

P = 125795.25/86400 = 1.456W

Answer 4

Hold on, I'll try to help..

a) Mass of blood = 7500x 1.05 =7875Kg (7.875 tonnes).

b) Force = mass x gravity = 7500 x 9.8= 77175N

c)Work done =mgh =7500 x 9.8 x 1.63 = 125795.25 J (125.8KJ)

d) In 24 hours there are 24x 60 x 60 seconds =86400seconds.

Power = Work/time = 125795.25/86400 =1.456 J/s (1.456W)