Why Does the Ramp Exert Total Force mg Instead of mgcos30 on the Mass?

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In summary, the question is asking for the total force exerted by the ramp on the block, which includes the friction and normal forces. The block is not moving, so the overall acceleration is zero. The correct force can be found by balancing the forces in the vertical direction, with gravity pulling down on the block with a force of mg. The normal force exerted by the ramp on the block is mgcos30, but the total force F must balance against the downward force mg.
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My exam is in an hour, so quick replies are dearly needed!

http://www.ph.qmul.ac.uk/phy116/Exams/Mid%20Term%20Test%202006%20Answers.pdf
Question 3)a

I would have said the force exerted by the RAMP on the MASS is mgcos30, not mg as my lecturer has said (and it's the same in every paper).

What am I not seeing here? The only thing I can think of is due to the axis of where F is.

Thanks!
 
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The block is not moving, thus a = 0. Also, gravity pulls down on the block with a force equal to mg. If you accept these two facts, balance the forces in the vertical direction and see what you get.
 
  • #3
I just saw this post, too late for the exam, but I have a comment that may help.

mg cos30 is the normal force exerted by the ramp on the block. But the question is really asking for the total force F exerted by the ramp, which includes the friction and normal forces.

As diazona said, F must balance against the downward, vertical force mg.
 

FAQ: Why Does the Ramp Exert Total Force mg Instead of mgcos30 on the Mass?

What is basic mechanics and why is it important?

Basic mechanics is the branch of physics that deals with the study of motion and the forces that cause it. It is important because it provides a foundation for understanding more advanced concepts in physics and is also applicable to many real-world situations, such as designing machines and structures.

What are the three laws of motion?

The three laws of motion, as stated by Sir Isaac Newton, are:
1. 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.
2. The force acting on an object is equal to its mass multiplied by its acceleration.
3. For every action, there is an equal and opposite reaction.

What is the difference between speed and velocity?

Speed is a measure of how fast an object is moving, while velocity also takes into account the direction of motion. In other words, velocity is speed with a specific direction attached to it.

How does friction affect motion?

Friction is a force that opposes motion and can cause objects to slow down or stop. It is caused by the interaction between two surfaces and is dependent on factors such as the roughness of the surfaces and the force pushing the objects together.

What is the difference between static and kinetic friction?

Static friction is the force that prevents an object from moving when a force is applied to it, while kinetic friction is the force that acts on an object in motion. The amount of static friction is usually greater than the amount of kinetic friction.

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