Physics Help?

Question

If friction is the only force acting on an object during a given physical process, which of the following assumptions can be made in regard to the object's kinetic energy?
a. The kinetic energy decreases
b. The kinetic energy increases
c. The kinetic energy remains constant
d. The kinetic energy decreases and then increases

Why?

Answer 1

If the object has a non zero velocity at the beginning of the process, the kinetic energy of that object decreases, because the velocity of that object decreases. That happens because heat is lost through friction. It has been observed in nature that the total energy of a system it remains constant in time. If one considers a system made of the environment and the object which goes through the physical process in that environment, one may consider the friction as a transfer of energy from the object to the environment. That leads to an increase in the environment's energy and a decrease in the object's energy (but the energy of the system made by the environment and the object is the same). I mention that the energy may exist in many forms (e.g. heat, kinetic energy, electric energy and so on) and it may turn from one form to another. A decrease in the object's energy means, in this case, a decrease in its kinetic energy. You can make a simple experiment to see that: you can try to launch a book on a table (you give a push to the book) and you will see that in a few seconds the book will reduce its velocity on the table (that unless the table is very slippery), which means that its kinetic energy decreases.

If the object that goes through a physical process has no velocity at the beginning of that process, the kinetic energy will remain constant, that is zero, because if it doesn't have velocity, it doesn't have kinetic energy either. A simple experiment: a book that sits on a table - there is friction between the table and the book, but the book has no velocity, and therefore no kinetic energy.

I hope this answer helps you. Good luck!

Answer 2

Assuming the ojbect is in motion, the kinetic energy decreases. This is because the friction acts as another force that attempts to bring the object to rest, thus reducing the kinetic energy.

Answer 3

A, Kinetic Energy Decreases. movement is defined as kinetic energy. Friction acts in the opposite way that forward momentum does so you will be slowing down, decreasing your movement, therefore decreasing your kinetic energy

Answer 4

Friction is a force that tries to prevent relative motion between any two surfaces. If a body's point of contact tries to move with respect to the surface, friction would try to stop the motion thus acting in the direction opposite to the existing velocity hence reducing it. And if it is the only force acting then it is certainly acting opposite to the direction of motion and trying to stop it.
Hence, the correct option is 'a.' The kinetic energy decreases.

Answer 5

friction slows the object down because friction is opposite direction of motions. As the object slows down, its Kinetic energy decreases.

Answer 6

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Answer 7

"a" because friction always opposes motion.