Question

A girl and a puppy are 540 feet apart when they start running towards each other. The girl runs at a speed of 15 feet per second, and the puppy runs at a speed of 12 feet per second. How soon will they meet?

Answer 1

Answer: 20 seconds

Explanation:

The distance is 540 feet

speed of the girl = 15ft/s

speed of the puppy = 12 ft/s

If we stand in the frame of reference where the girl is still, in this frame the speed of the puppy will be equal to the speed of the puppy in our previus frame plus the speed of the girl in the previous frame (because they are running in opposite directions)

S = 15 ft/s + 12ft/s = 27ft/s

Now we can use the equation:

time = distance/speed

T = 540ft/27ft/s = 20s