A woman stands on a moving sidewalk (conveyor belt) that is moving to the right at a speed of 2 m/s relative to the ground. A dog runs on the belt toward the woman at a speed of 8 m/s relative to the belt. A conveyor belt is moving to the right at the speed v subscript belt, ground equals 2 meters per second. A girl stands stationary on the left end of the belt. A dog runs on the belt to the left toward the girl at the speed v subscript dog, belt equals 8 meters per second. What is the speed of the dog relative to the ground

   V_{2G} = - 10 m / s

Explanation:

This is an exercise on relative velocities in one dimension, let's use the subscript 1 for the girl, the 2 for the but, the index 3 for the conveyor belt and the index G for the Earth

we will consider the velocity is positive to the right.

They indicate the speed of the belt with respect to the ground = 2 m/s

   the dog speed with respect to the belt = - 8 m / s

Dog speed is requested with respect to the Earth

notice that the inner subscripts cancel out.

We calculate

            = -8 - 2

            V_{2G} = - 10 m / s

the negative sign indicates that the dog moves to the left

pythagoras' theorem

square root (-5^2+9^2)

square root (25+81)

square root (106)

angle is tan^-1(9/5)

neg x, pos y