Question

Which of the following is ALWAYS true.

a) An object experiencing a constant negative acceleration has a decreasing momentum.

b) If an object has a constant acceleration, its kinetic energy is changing at a constant rate.

c) If an object has a zero net force acting on it, its kinetic energy is constant.

d) If an object's kinetic energy is constant, there is no net force acting on it.

e) If an object's kinetic energy is increasing there is a positive net force on it.

Answer 1

Momentum = m*v
For constant negative acceleration -
As Vf < Vi
Final Momentum < Initial Momentum
So,
a) An object experiencing a constant negative acceleration has a decreasing momentum. = Allways True.


Kinetic Energy = 1/2*mv^2

b) If an object has a constant acceleration, its kinetic energy is changing at a constant rate. = Not Allways True.

Force = Mass * Acceleration
For Zero Force , Acceleration = 0
Therefore Velocity will remain Constant.
Kinetic Energy = 1/2*mv^2
So Kinetic Energy will also Remain constant.

c) If an object has a zero net force acting on it, its kinetic energy is constant. =  Allways True.



Kinetic Energy = 1/2*mv^2
If an object's kinetic energy is constant then Velocity is Constant.
Which Means Acceleration = 0
Therefore Force = Mass * Acceleration
Force = 0.

d) If an object's kinetic energy is constant, there is no net force acting on it. - Allways True.

If the kinetic energy increases, the change in kinetic energy will be positive , work done will be positve.
Work done = Force * Distance
Therefore Force will be Positive.

e) If an object's kinetic energy is increasing there is a positive net force on it - - Allways True.