Final answer:
To find Pat's speed relative to the water, we subtract the speed at which Pat is walking from the speed of the boat. Since Pat is walking towards the back at 5 km/hr against the boat's forward speed of 30 km/hr, Pat's relative speed to the water is 25 km/hr.
Step-by-step explanation:
The question you've asked pertains to the concept of relative velocity in physics. As Pat is a passenger moving on a boat, we need to consider Pat's speed relative to the water. Given the boat is moving at 30 km/hr and Pat is walking towards the back (opposite to the direction of the boat's motion) at 5 km/hr, we calculate Pat's speed relative to the water by subtracting Pat's speed from the boat's speed. So, Pat's speed relative to the water is 30 km/hr - 5 km/hr = 25 km/hr.