It depends on the type of question, mechanical condition and given values,
You can use the formula,
Coefficient of kinetic friction = Force of Kinetic friction / Normal force (perpendicular to contacting surfaces)
Hope this helps!
Dark energy is what is causing the accelerating expansion of the universe. It can also be defined as the theoretical energy that counteracts or acts against gravity. Others also define it as a theoretical, new kind of dynamic energy field that fills space, but whose energy has an effect opposite to that of normal energy.
Answer:

Explanation:
The motion of the skater is a uniformly accelerated motion, so we can find the deceleration by using the following suvat equation:

where
v is the final velocity
u is the initial velocity
a is the acceleration
s is the displacement
In this problem, we have:
u = 19 m/s is the initial velocity of the skater
v = 18 m/s is the final velocity of the skater
s = 2.0 m is the displacement
Solving for a, we can find the acceleration:

And the negative sign tells us that the acceleration is in the opposite direction to the motion (so, it is a deceleration)