What is speed and velocity​

The distance covered by the body per unit time is called speed.

A distance travelled by the body per unit time in a fixed direction is called velocity

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Force is an external agency that changes or tends to change the state of a body from rest to motion or from motion to rest is called force

Explanation:

The distance covered by a body in a unit time is called speed

a police officer and a ambulance

nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.