Forces and Newton's Laws of Motion

In summary: Now, to keep the small cube from sliding down, the force of friction between the two cubes must be equal to the force pulling the large cube. This means that the force of friction is equal to P, since P is the only force acting on the large cube. So, we can set up the equation: Ffriction = f*msmall*g = P. Plugging in the given values, we get P = (0.71)*(4 kg)*(9.8 m/s^2) = 27.616 N. However, this is the minimum force needed to keep the small cube from sliding. Since we want to know the smallest magnitude that P can have, we need to find the maximum force that P can have without
  • #1
kaspis245
189
1

Homework Statement


The drawing shows a large cube (mass = 25 kg) being accelerated across a horizontal frictionless surface by a horizontal force P. A small cube (msmall = 4 kg) is in contact with the front surface of the large cube and will slide downward unless P is sufficiently large. The coefficient of friction between the cubes is f = 0.71 . What is the smallest magnitude that P can have in order to keep the small cube from sliding down?

image.jpg


Homework Equations


Ffriction= f*mg

The Attempt at a Solution


Ffriction=msmall*g
f*P=msmall*g
P=56,34N

But the answer must be P = 400 N.
 
Physics news on Phys.org
  • #2
P has to accelerate both the small and the large block, that will take more force than the force between the two blocks.
 
  • #3
Great answer but still not clear.
 
  • #4
kaspis245 said:
Ffriction=msmall*g
f*P=msmall*g
P=56,34N
What you found is the force that must push against the small mass, not P, which is the force that pulls the large mass. Use what you found to figure out what P must be.
 
  • #5
I kinda figured that out. Can somebody show me how to do it?
 
  • #6
Here's a hint: Consider the acceleration.
 
  • #7
You mean P = ma ?
 
  • #8
kaspis245 said:
You mean P = ma ?
Yes. Well, F = ma. Consider the acceleration of the small mass first.
 
  • #9
The acceleration of the small mass is equal to the large mass.
 
  • #10
kaspis245 said:
The acceleration of the small mass is equal to the large mass.
Exactly! What's the acceleration of the small mass?
 
  • #11
The acceleration of the small mass a = P/msmall
 
  • #12
Got it. asmall = 14 m/s2

Plarge = (m + msmall)*a = 400 N
 
  • #13
kaspis245 said:
The acceleration of the small mass a = P/msmall
No. It's the force acting on the small mass divided by the small mass.
 
  • #14
kaspis245 said:
Got it. asmall = 14 m/s2

Plarge = (m + msmall)*a = 400 N
Good!
 

1. What are the three laws of motion?

The three laws of motion, also known as Newton's laws of motion, are the fundamental principles that govern the motion of objects. The first law states that an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity, unless acted upon by an external force. The second law states that the force applied to an object is equal to its mass multiplied by its acceleration. The third law states that for every action, there is an equal and opposite reaction.

2. How do forces affect motion?

Forces can cause changes in an object's motion by either changing its speed, direction, or both. Forces can either cause an object to accelerate or decelerate, depending on the direction of the force relative to the object's motion. In the absence of external forces, an object will continue to move in a straight line at a constant speed.

3. What is the difference between mass and weight?

Mass is a measure of the amount of matter in an object, while weight is a measure of the force of gravity acting on an object. Mass is an intrinsic property of an object and remains constant regardless of its location, while weight can vary depending on the strength of the gravitational pull.

4. Can an object be in equilibrium if there are multiple forces acting on it?

Yes, an object can be in equilibrium if the vector sum of all the forces acting on it is zero. This means that the forces are balanced, and the object will either remain at rest or continue to move at a constant velocity.

5. How do Newton's laws of motion apply to real-life situations?

Newton's laws of motion can be applied to a wide range of real-life situations, from the motion of objects on Earth to the motion of celestial bodies in space. These laws help explain why objects move the way they do and allow us to predict and control their motion. They are also essential in fields such as engineering, aerodynamics, and space exploration.

Similar threads

Newton's law problem: Pushing 2 stacked blocks on a horizontal table
    • Introductory Physics Homework Help
Replies
13
Views
970
Newton's Second Law (Pulley Sustem)
    • Introductory Physics Homework Help
Replies
3
Views
799
Newton's laws--Block sliding up a frictionless semi-circular track
    • Introductory Physics Homework Help
2
Replies
37
Views
2K
Newton's 2nd Law: Why is Resistance Considered a Positive Force?
    • Introductory Physics Homework Help
Replies
3
Views
963
Acceleration and Gravity with Circular Motion
    • Introductory Physics Homework Help
Replies
9
Views
2K
Having a hard time learning Newton's 2nd law
    • Introductory Physics Homework Help
Replies
5
Views
376
Solving for Masses in an Atwood Machine
    • Introductory Physics Homework Help
Replies
8
Views
594
How to find Potential Energy without distance
    • Introductory Physics Homework Help
Replies
4
Views
3K
Explanation for Newton II giving negative mass in my Physics lab results please
    • Introductory Physics Homework Help
2
Replies
44
Views
1K
Unbalanced force to find altitude of airplane
    • Introductory Physics Homework Help
Replies
4
Views
1K

Hot Threads

Recent Insights

Back
Top