For which of the following is the velocity constant (speed/direction does not change)? a) a cat escaping a dog by running in a straight line and then up a tree at a constant speed of 30 mph b) a cat escaping a dog by running in a straight line away from the dog and slowing down when danger is gone. c) a cat escaping a dog by running at a constant speed around and around the house until the dog gets bored. d) a cat ignoring the dog by sitting perfectly still.

The answer is D. Velocity has a direction and a magnitude, so to have a constant velocity, none of them should be changing. A seems right at first, but when the cat climbs up a tree, it's changing directions. B says the cat slows down which means there's a change in velocity and acceleration is present. C says that the cat's running around in circles so it's constantly changing directions. D is the only right one because the magnitude of velocity (speed) is 0 and not changing neither is the direction. 

Hope this makes sense!

Change in speed or direction : )

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