#### Answer

0.02 N.

#### Work Step by Step

Find the average acceleration of the blood.
$$\frac{0.35 m/s – 0.25 m/s}{0.10 s}=1.0 \frac{m}{s^{2}}$$
Use Newton’s second law to find the required net force on the blood, exerted by the heart muscle. The answer is rounded to 2 significant figures.
$$\Sigma F=ma=(0.020 kg)(1.0 \frac{m}{s^{2}})= 0.02 N $$