Newton's Second Law Question

Question

Assume that during each pulse a mammalian heart accelerates 21.0 g of blood from 18.0 cm/s to 0.28 m/s during a time interval of 0.100 s. Calculate the magnitude of the force exerted by the heart muscle on the blood

Answer 1

Solution:

Find the pulse acceleration. Note that the initial velocity is given in cm/s , so convert to m /s,

V_i = 18 cm/s ( m /100 cm) = 0.18 m/s, the final velocity is given as V_f = 0.28 m/s, therefore the acceleration is the change in velocity per unit time a = Δ V / t = ( V_f - V _i) / t = (0.28 m/s - 0.18 m/s) / 0.1 s = 1 m/s²

The Force required to pump the blood is F = m a, where m is the mass of the blood given in grams which you need to convert to kg

m = 21 g ( 1 kg / 1000 g) = 0.021 kg, and F = 0.021 kg ( 1 m/s²) = 0.021 N