Answer:

Explanation:
The work done on a particle by external forces is defined as:

According to Newton's second law
. Thus:

Acceleration is defined as the derivative of the speed with respect to time:

Speed is defined as the derivative of the position with respect to time:

Kinetic energy is defined as
:

Answer:
Please find the answer in the explanation
Explanation:
Friction is a force that opposes motion. One or two of the advantages of friction are break and ability of an object to walk.
Writing yes it is useful because when your writing because friction helps you see what your writing
ii. Rubbing. Yes, it is useful.
friction make it possible for two object to rub each other
iii. Skiing. No. It is not useful because With presence of friction, skiing will not be possible.
iv. Rotating a wheel No. It is not useful because Friction will oppose the rotation of the wheel.