Can you find the applied force with just the initial and final velocties?

In summary, the conversation revolved around creating a challenging physics problem involving a ball rolling down a carpeted decline. However, due to the lack of information given, such as the mass of the ball, it was concluded that the problem is unsolvable. Suggestions were made to incorporate the coefficient of rolling resistance and the ball's radius in order to potentially solve the problem. The conversation also touched upon the concept of dimensional analysis and how it can be used to determine the necessary information for solving a problem involving force.
  • #1
glenohumeral13
6
0

Homework Statement


I'm trying to create a problem for my physics standards that is hard. I gave myself a ball being pushed down a carpeted decline at 24° from the horizontal. The balls starts with an initial velocity of 1 m/s and ends the 6 meter decline at 5 m/s. I want to find the applied force on the ball.

Homework Equations


Perhaps "1/2vf2 = g*hi"?

The Attempt at a Solution


Found a stalemate because I don't want to give the mass, or else the problem is too easy. So, I can't use "Fg = m*ag".
 
Physics news on Phys.org
  • #2
Do you know about dimensional analysis? This would tell you that force involves a mass dimension, so you cannot calculate a force from only distance and time dimensions.
(Why a ball? Wouldn't a ball roll?)
 
  • #3
I assume that you mean the rolling friction force of the ball with the carpeted incline... (?)
 
  • #4
haruspex said:
Do you know about dimensional analysis? This would tell you that force involves a mass dimension, so you cannot calculate a force from only distance and time dimensions.
(Why a ball? Wouldn't a ball roll?)
Okay. Thanks.
Yeah, it probably should have been a block.
 
  • #5
NTW said:
I assume that you mean the rolling friction force of the ball with the carpeted incline... (?)
Could I find that with the given information?
 
  • #6
glenohumeral13 said:
Could I find that with the given information?
No. The problem is unsolvable - in the same way the question "I am in a car and accelerate. It is 2 pm. Find the mass of the car" is not solvable.
 
  • #7
glenohumeral13 said:
Could I find that with the given information?

I'm not sure... Let's see... The final velocity of the ball will be the same in free fall or rolling with no resistance along the incline. That velocity would be v = SQR (2 * 9,81 * 6 m * sin 24º) = 6,91 m/s. You state that there is an extra initial velocity of 1 m/s, so we would have a total of 7,91 m/s.

But 5 m/s is mentioned in the problem as final velocity. Thus, there is a braking force. It could come from rolling resistance and from rotational kinetic energy acquired by the ball during its run... Rolling resistance is a function of the mass of the ball, g, the angle and a coefficient mu. Rotational kinetic energy is a function of the angular velocity w, itself a funcion of v and the ball's radius r, and of the moment of inertia of a sphere 2/5 * m* r^2

Mass is not given. It might cancel away, I'm not sure, but the problem could perhaps be solved 'by energies', deriving the solution also in terms of the unknown magnitudes, maybe m (if it doesn't cancel away), a coefficient of rolling resistance mu, and the ball's radius r...

That, in case it can be solved at all... I am myself a solver of easy problems only...
 
  • #8
NTW said:
I'm not sure... Let's see...
As I wrote in post #2, dimensional analysis proves there is not enough information. You have to be given a quantity with a mass dimension - could be mass, force, energy, momentum..., but distances times and accelerations by themselves cannot do it.
 
  • #9
mfb said:
No. The problem is unsolvable - in the same way the question "I am in a car and accelerate. It is 2 pm. Find the mass of the car" is not solvable.
Haha. Okay. Thanks everybody. I'll just do something with μk and the coefficient then.
 

Related to Can you find the applied force with just the initial and final velocties?

1. How do you calculate the applied force with just the initial and final velocities?

To find the applied force, you can use the formula F=ma, where F is the force, m is the mass of the object, and a is the acceleration. The initial and final velocities can then be used to calculate the acceleration using the formula a=(vf-vi)/t, where vf is the final velocity, vi is the initial velocity, and t is the time interval. Once you have the acceleration, you can plug it into the formula F=ma to find the applied force.

2. Can the applied force be found if the time interval is not given?

No, the time interval is necessary to calculate the acceleration and therefore the applied force. If the time interval is not given, the applied force cannot be determined with just the initial and final velocities.

3. Is the applied force the same as the net force?

Not necessarily. The applied force is the force that is directly applied to the object, while the net force is the sum of all the forces acting on the object. The net force can include other forces such as friction or gravity, while the applied force only considers the force being applied to the object.

4. Can you find the applied force if the mass of the object is not given?

No, the mass of the object is a necessary component in calculating the applied force. Without knowing the mass, the applied force cannot be determined with just the initial and final velocities.

5. How accurate is the calculation of the applied force using just the initial and final velocities?

The accuracy of the calculation depends on the accuracy of the initial and final velocities and the time interval. If these values are measured and recorded accurately, the calculated applied force should also be accurate. However, other factors such as air resistance or external forces may affect the accuracy of the calculation.

Similar threads

Final Velocity of a car with a opposing decreasing drag force
    • Introductory Physics Homework Help
2
Replies
57
Views
746
Why can we move the spring with constant speed when we apply a force?
    • Introductory Physics Homework Help
Replies
29
Views
995
Newton's 2nd Law: Why is Resistance Considered a Positive Force?
    • Introductory Physics Homework Help
Replies
3
Views
985
Questions Regarding a Cat Going Up a Ramp
    • Introductory Physics Homework Help
2
Replies
56
Views
2K
Applied force of a ball on a glove
    • Introductory Physics Homework Help
Replies
8
Views
3K
Calculating Theoretical Reaction Force of Ball Traveling in Semi-Circle
    • Introductory Physics Homework Help
2
Replies
43
Views
2K
Force applied on the pulley of a system
    • Introductory Physics Homework Help
Replies
8
Views
2K
Block on a Spring, Nonconstant Net Force
    • Introductory Physics Homework Help
Replies
6
Views
996
Applying a force in a wheel bicycle
    • Introductory Physics Homework Help
Replies
2
Views
879
Find the unkown tensions and masses in the situation below
    • Introductory Physics Homework Help
Replies
8
Views
424

Hot Threads

Recent Insights

Back
Top