What Is the Coefficient of Friction for Fred's Rollerblades?

In summary: Then use the formula F = ma to find the force of friction. Finally, use the formula Ff = µk FN to solve for µk. So, in summary, to find the coefficient of friction between Fred's rollerblades and the ground, we need to find the magnitude of the acceleration, which can be found using the initial and final velocities and the time. Then, using the formula F = ma, we can find the force of friction. Finally, using the formula Ff = µk FN, we can solve for µk.
  • #1
NeomiXD
31
0
Fred (60 kg) is rollerblading at a velocity of 25 km/h [E] when he sees a broken glass bottle on the path ahead. He brakes and is slowed to a velocity of 8 km/h [E] in 4.2 s. What is the coefficient of friction between Fred's rollerblades and the ground? (Hint: Find FN and Ff first.)

Given:

m = 60 kg
v1 = 25km/h = 6.94m/s [E]
v2 = 8km/h = 2.20m/s [E]
Δt = 4.2s
g = 9.8 N/kg

Required:

?

Solution:

Fg = mg
Fg = (60kg) (9.8 N/kg)
Fg = 588 N

FN = Fg
FN = 588 N
Ff ≤ µs FN
Ff ≤ µs (588 N)

??

I don't know what to do after.
µs is not given, so how do you solve this question?
 
Physics news on Phys.org
  • #2
His initial kinetic energy must be equal to his final kinetic energy plus the amount of energy lost due to friction. So the amount of energy lost to friction is [itex]E_{ki} - E_{kf}[/itex] which is equal to [itex]mg\mu d[/itex]. Now you were given time instead of distance, but if you can assume constant deceleration, you could get d.
 
  • #3
Hints: What's the skater's acceleration while applying the brakes? How much force is needed to create such an acceleration?
 
  • #4
Am I looking fo µs or µk?
 
  • #5
I would say you're looking for [itex]\mu k[/itex], as [itex]\mu s[/itex] is only applicable when masses have zero velocity. To solve for [itex]\mu s[/itex], you need to be told how much force is being applied to a body at rest when it just starts to budge.
 
  • #6
So, if I'm solving for µk, how do I find Ff (the force of friction)? What formula do I have to use?
 
  • #7
The force of friction is equal to the normal force multiplied by the kinetic coefficient of friction. The normal force is equal (in magnitude, but opposite in direction) to the force pulling the object down, namely, mg.
 
  • #8
NeomiXD said:
Am I looking fo µs or µk?

If the wheels on the roller-blades do not skid on the ground, then you are working with µs. If the wheels are skidding, then you have µk .
 
  • #9
Think kinematics. You have an initial velocity, a final velocity, and a time. Use this information to find the magnitude of the acceleration.
 

FAQ: What Is the Coefficient of Friction for Fred's Rollerblades?

What is force of gravity?

Force of gravity, also known as gravitational force, is the force that attracts objects with mass towards one another. It is one of the four fundamental forces of nature and is responsible for keeping the planets in orbit around the sun and objects on Earth from floating off into space.

How is force of gravity calculated?

The force of gravity can be calculated using Newton's Law of Universal Gravitation, which states that the force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. This can be expressed as F = G(m1m2)/d^2, where F is the force of gravity, G is the gravitational constant, m1 and m2 are the masses of the two objects, and d is the distance between them.

Does force of gravity vary on different planets?

Yes, force of gravity varies on different planets due to differences in mass and distance. The larger the mass of a planet, the stronger its gravitational force, and the farther an object is from the planet's center, the weaker the force of gravity will be. For example, the force of gravity on Earth is stronger than on the Moon due to Earth's larger mass and closer distance to the object.

Can force of gravity be manipulated?

No, force of gravity cannot be manipulated. It is a naturally occurring force and is always present between any two objects with mass. However, the effects of gravity can be counteracted by other forces, such as lift or thrust, to allow objects to overcome the force of gravity and move through space.

What would happen if there was no force of gravity?

If there was no force of gravity, objects with mass would not be attracted to one another. This would result in a lack of structure in the universe, as planets and stars would not be held together by gravity. Additionally, life as we know it would not exist, as gravity plays a crucial role in the formation and function of living organisms on Earth.

Similar threads

Yes! Calculating Friction Coefficient
Replies
1
Views
994
Calculating Net Force and Friction: Understanding Newton's Laws of Motion
Replies
9
Views
2K
Coefficient of Friction when Normal Force is Reduced [HS]
Replies
5
Views
1K
Find the force of Friction and minimum coefficient of friction
Replies
1
Views
1K
Coefficient of Friction question for a cart going down a wooden ramp
Replies
18
Views
2K
Weight in an elevator? Free body diagrams
Replies
1
Views
2K
Complex Kinematics and Dynamics
Replies
8
Views
1K
Complex Kinematics and Dynamics
Replies
7
Views
1K
How Do You Calculate the Weight of a Block on an Inclined Plane?
Replies
6
Views
3K
Find the force to push a book sideways on a table
Replies
2
Views
2K

Hot Threads

Recent Insights

Back
Top