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

because growing process had stoped after 4-5 year

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.