Tough question about reaction force Newton's third law -- Please help

In summary, the conversation discusses the calculation of force necessary to produce a specific acceleration in a given block using the equation F=ma. The confusion arises between the abstract "F" and the specific "F" in the problem, and it is mentioned that using the mass 3m instead of 5m will also yield the correct answer. It is emphasized that all relevant forces must be taken into account and the algebra must be done correctly to obtain the correct solution.
  • #1
14
0

Homework Statement


. question is as attached. answer is 2f/5..how do u get this?

Homework Equations


F=ma
F= (5m)a
a= F/(5m)

The Attempt at a Solution


gotten a=F/5m , but why the answer is 2f/5?
 

Attachments

  • Screen Shot 2015-01-09 at 1.09.40 AM.png
    Screen Shot 2015-01-09 at 1.09.40 AM.png
    49.9 KB · Views: 1,024
Physics news on Phys.org
  • #2
What force is necessary to produce your calculated acceleration in the second block?
 
  • #3
F?
 
  • #4
No... you calculated the specific ##a##, now put that back into ##F=ma## along with the second block's mass

Unfortunately the confusion between the abstract "F" and the specific "F" in this problem is perhaps making understanding a little harder than it should be.
 
  • #5
I see. Why not use the mass 3m?
 
  • #6
bomberkid said:
I see. Why not use the mass 3m?
Either will do provided you bring all relevant forces acting on the mass into the equation.
 
  • #7
but if i were to use f=3m, and a is F/5m, i wouldn't get 2f/5 as the answer
 
  • #8
bomberkid said:
but if i were to use f=3m, and a is F/5m, i wouldn't get 2f/5 as the answer
You get the right answer if you bring in all forces acting on the mass and do the algebra correctly. Please post your working.
 

1. What is Newton's third law?

Newton's third law states that for every action, there is an equal and opposite reaction. This means that when an object exerts a force on another object, the second object will exert an equal and opposite force back on the first object.

2. How does this relate to reaction force?

The reaction force is the force exerted by the second object in response to the action force. According to Newton's third law, this reaction force will be equal in magnitude but opposite in direction to the action force.

3. Can you give an example of Newton's third law in action?

One example is when you push against a wall, the wall pushes back on you with an equal and opposite force, preventing you from moving through the wall.

4. Does Newton's third law only apply to objects in contact?

No, Newton's third law applies to all objects, whether they are in contact or not. For example, when a rocket propels itself forward, the exhaust gases are pushing against the rocket with an equal and opposite force.

5. How does Newton's third law impact everyday life?

Newton's third law can be observed in many everyday situations, such as walking, swimming, and driving a car. It also plays a crucial role in the design and function of various machines and structures, from bicycles to skyscrapers.

Suggested for: Tough question about reaction force Newton's third law -- Please help

Back
Top