Integrated Concepts

The 70.0-kg swimmer in Figure 7.44 starts a race with an initial velocity of 1.25 m/s and exerts an average force of 80.0 N backward with his arms during each 1.80 m long stroke. (a) What is his initial acceleration if water resistance is 45.0 N? (b) What is the subsequent average resistance force from the water during the 5.00 s it takes him to reach his top velocity of 2.50 m/s? (c) Discuss whether water resistance seems to increase linearly with velocity.

Solution

Step 1 of 3

a) Consider a swimmer is swimming with initial velocity and exerts an average force of backward with his hands during each long stroke.

We need to find out his initial acceleration if water resistance is .

The net force

Work done by the swimmer

The work done is the kinetic energy of the swimmer can write as,

Implies

The mass of the swimmer

We know that