Newton's Third law of motion problem.

In summary, the problem involves an object moving on a table with a constant friction force opposing its motion. Two different applied forces, 10 N and 20 N, result in accelerations of 2 m/s2 and 6 m/s2, respectively. To find the force of friction, we need to use Newton's 2nd law, F=ma, and the equation for friction force, F=μS. This results in a system of equations with two unknowns, which we can solve to find the force of friction.
  • #1
abrowaqas
114
0

Homework Statement


An object is free to move on a table, ex-
cept that there is a constant friction force f
that opposes the motion of the object when
it moves. If a force of 10 N pulls the object
across the table, the acceleration is 2 m/s2. If
a force of 20 N pulls the object across the ta-
ble, the acceleration is 6 m/s2. What is the
force of friction f?

a) 3.33 N
b) 1 N
c) 5 N
d) 10 N
e) none of these

Homework Equations



F= ma
and
F= -F'

and
F= μS where μ= coefficient of static friction

The Attempt at a Solution



i first find the mass in both case

F= 10 N and a= 2m/s/s
so
m= F/a = 10/2
m= 5kg

and again

F= 20N and a= 6m/s/s

so
m= F/a = 20/6
m= 3.33kg

what i do next..
or
either i must go to

F= μ S

please help me to solve it.. how i go further?
 
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  • #2
abrowaqas said:
F= 10 N and a= 2m/s/s
so
m= F/a = 10/2
m= 5kg
10 N is the applied force, not the net force. To use Newton's 2nd law you need the net force.
 
  • #3
then Doc Al

how will i find the net force..
will it be

Fnet = 20+10 = 30N ...
what i do next?
 
  • #4
abrowaqas said:
how will i find the net force..
will it be

Fnet = 20+10 = 30N ...
No. In the first case, what two forces act? One is the applied force of 10 N. What's the other force?

You'll end up with an equation with 2 unknowns.

Then you'll get a second equation, using the second case (with the applied force of 20 N).

You'll solve those two equations for the two unknowns.
 
  • #5


I would approach this problem by first identifying the key variables and principles at play. The key variables in this problem are force, acceleration, and friction. The principle that applies is Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction.

Using the information given, we can see that the force of 10 N and 20 N are the actions, and the resulting acceleration of 2 m/s2 and 6 m/s2 are the reactions. This means that there must be an equal and opposite force acting on the object to produce these accelerations. This force is the force of friction, which is opposing the motion of the object.

To find the force of friction, we can use the equation F=ma. In this case, the force we are looking for is the force of friction, and the acceleration is the given values of 2 m/s2 and 6 m/s2. We can rearrange the equation to solve for F, which gives us F=m*a.

Plugging in the values for mass (5 kg and 3.33 kg), we can calculate the force of friction for each scenario. For the first scenario, with a force of 10 N and an acceleration of 2 m/s2, the force of friction would be 10 N. For the second scenario, with a force of 20 N and an acceleration of 6 m/s2, the force of friction would be 20 N.

Therefore, the correct answer is d) 10 N.

It is important to note that the force of friction is dependent on the mass of the object, as seen in the different values calculated for the different masses. It is also important to consider the coefficient of friction, which is a constant that depends on the surfaces in contact. In this case, the coefficient of friction is not given, so we cannot calculate the exact value of the force of friction. However, we can confidently say that the force of friction will always be equal and opposite to the applied force, as per Newton's Third Law.
 

FAQ: Newton's Third law of motion problem.

1. What is Newton's Third Law of Motion?

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that whenever an object exerts a force on another object, the second object exerts an equal and opposite force back on the first object.

2. How does Newton's Third Law apply to real-life situations?

Newton's Third Law can be seen in many real-life situations, such as when you push on a wall, the wall pushes back on you with an equal force. It also explains how rockets are able to launch into space by expelling gas in one direction, causing the rocket to move in the opposite direction.

3. Can you provide an example of Newton's Third Law in action?

One example of Newton's Third Law is a person rowing a boat. As they pull the oar through the water, the oar exerts a force on the water, pushing it backwards. In return, the water exerts an equal and opposite force on the oar, propelling the boat forward.

4. How does Newton's Third Law relate to forces?

Newton's Third Law explains that forces always occur in pairs. This means that whenever one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object.

5. Are there any exceptions to Newton's Third Law?

No, there are no exceptions to Newton's Third Law. It is a fundamental principle of physics that applies to all objects and forces, regardless of their size, shape, or speed.

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