# Calculate the time of a swimmer

1. Aug 30, 2011

### tavo0116

A child, who is 45 m from the bank of a river, is being carried helplessly downstream by the river's swift current of 1.0 m/s . As the child passes a lifeguard on the river's bank, the lifeguard starts swimming in a straight line until she reaches the child at a point downstream.

a)If the lifeguard can swim at a speed of 2.0 m/s relative to the water, how long does it take her to reach the child?
b)How far downstream does the lifeguard intercept the child?

Which equation should I use?

Thank you

2. Aug 30, 2011

### collinsmark

Displacement equals velocity times time. Combine that with the Pythagorean theorem.

(Hint: The displacements involved form a triangle)

3. Aug 30, 2011

### collinsmark

(Another hint: This problem is a little bit tricky, because the given speed at which the lifeguard can swim is 2 m/s relative to the water. So before you figure out the final answer, you'll have to to take this into account.)