Dynamics Problem HELP - Free body diagram

In summary: But then you do it again! You say "F= Ma" and then say "46g * 44.9 m/s2"! You are using "g" as if it were a force, which it is not. You multiplied "g" by mass so your answer does have the right units (Newtons) but it is the wrong number. You should not multiply "g" by mass to get a force. You should multiply mass by acceleration to get a force. In this case the mass is 46 grams and the acceleration is 44.9 m/s2. When you multiply those together you get a force, which is 2.065 Newtons.In summary,
  • #1
coglon
8
0
IM in Phys.20 Got this question for an assignment. Tried it and got stuck. I really need help
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When golfing, uphill and downhill putts present different levels of difficulty. Suppose a green has a 5.0 degree slope and the force of friction will be 0.10N against the ball's motion. The ball has a mass of 46g and the length of putt will be 10.0m.

Which putt (uphill or downhill) presents a greater level of difficulty? Explain your reasoing using appropriate calculations

Draw Free body diagrams for both purrs. Find range of speed you may give the ball on each type of putt so that even if you miss the ball will stop within 1.0m of the hole.
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I know uphill would be more difficult because it requires more force but I am having a hard time proving this using Free body diagrams and mathematical reasoning.
THANKS FOR THE HELP,
Coglon
 
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  • #2
Dynamics -- Still stuck.. need ideas

Fm=Fa+Fg
46^2=Fa+9.81^2
Fa=[squ]2019.7639
fa= 44.9m/s^2
F=Ma
=46g*44.9m/s^2
=2065N

Using Free body diagrams I believe I figured out that it would take...
43.8N downhill and 64.3N uphill
------------------
Im not sure if the above calculation are at all close and I cannot show you my Free Body Diagram due to the attach file would be too large and would not be readable to fit in attachment... I am have no clue how to determine the range of speed used to get the putt within 1.0m and whether or not I should be using some kinematic equations.

Thanks for help,
Coglon
 
  • #3


Hi coglon,

welcome to the forums.

This is an interresting problem...

Originally posted by coglon
Fm=Fa+Fg
46^2=Fa+9.81^2
Fa=[squ]2019.7639
fa= 44.9m/s^2
F=Ma
=46g*44.9m/s^2
=2065N

Uh, not exactly sure what you're trying to do here. What do Fm, Fa, and Fg represent?

You also need to check your units. A Newton is 1kg*1m/s2, not 1g*1m/s2

Using Free body diagrams I believe I figured out that it would take...
43.8N downhill and 64.3N uphill

You aren't going to be able to supply it with a force over the entire length of the path. The problem is assuming you bump it to give it an initial velocity (not caring the physics of the bump), and then applying friction and gravity forces to slow down/speed up the ball.

------------------
Im not sure if the above calculation are at all close and I cannot show you my Free Body Diagram due to the attach file would be too large and would not be readable to fit in attachment...

What type of file is it?

I am have no clue how to determine the range of speed used to get the putt within 1.0m and whether or not I should be using some kinematic equations.

The way I see it, you'll need to do 4 different equations for two different cases. You will know the final velocity (0), and through the free body diagrams you can find the total force for the two cases. You'll be solving for initial velocities given a final position of 9m and 11m (one meter past the hole and one meter in front of the hole) for each case.
 
  • #4
I will second enigma in his wondering if you really have looked carefully at what you are doing. In addition to writing Fm= Fa+Fg without telling us what Fm, Fa, Fg mean (I would guess that Fg is "force of gravity", perhaps Fm is the net force on the ball. Would Fa be the friction force?) you have replaced Fm with (46)2 and Fg with (9.81)2. The only "46" in the problem is mass of the ball: 46 grams and I would guess that "9.81" is the acceleration due to gravity. Neither (46g)2 nor (9.81 m/s2)2 is a force and since they don't have the same units, they certainly would not fit into that equation no matter what Fm, Fa, or Fg were supposed to be.
 

What is a free body diagram?

A free body diagram is a visual representation used in physics to analyze the forces acting on a single object. It shows all the external forces acting on the object and their direction, allowing for an easier understanding of the dynamics of the object.

Why is a free body diagram important?

A free body diagram is important because it helps to identify and analyze the forces acting on an object. This allows for a better understanding of the object's motion and enables the application of Newton's laws of motion to solve complex dynamics problems.

How do you draw a free body diagram?

To draw a free body diagram, first identify the object and all the forces acting on it. Then, draw a simple diagram of the object and label all the forces acting on it, including their direction and magnitude. It is important to choose a coordinate system and stick to it when drawing a free body diagram.

What is the difference between a free body diagram and a force diagram?

A free body diagram shows all the forces acting on an object, both external and internal, while a force diagram only shows the external forces. Additionally, a free body diagram includes the direction and magnitude of the forces, while a force diagram only shows the direction of the forces.

How do you use a free body diagram to solve a dynamics problem?

To solve a dynamics problem using a free body diagram, first identify and draw the free body diagram for the object. Then, apply Newton's laws of motion to analyze the forces and determine the acceleration of the object. Finally, use kinematic equations to solve for the motion of the object.

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