Answer :

A person walks 3.5 mph is speed. A bird flies 20 m/ s speed. A bird goes 30 m/s toward town is velocity.

Speed is define as the rate at which an object is moving along a path.speed is a scalar quantity.the average speed of object will continue same if the objects changes its direction. speed never be zero.

Velocity is define as the rate at which an object changes in certain direction.velocity is a vector quantity.velocity changes with time. velocity can be zero , negative or positive.

In the given case,

A person walks 3.5 mph .

this only ha magnitude, so, this is speed (s).

A bird flies 20 m/s .

this only has magnitude, so, this is speed.(s)

A bike goes 30 m/s toward town.

this has magnitude as well as direction.so, this is velocity (v)

Thus,A person walks 3.5 mph is speed. A bird flies 20 m/ s speed. A bird goes 30 m/s toward town is velocity.

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