Star Characteristic Questions What are the two things that stars are emitting into space?
1 answer:
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a)
Here the crate is moving at constant velocity, so no acceleration:
a = 0
Let's analyze the forces acting along the horizontal and vertical direction.
- Vertical direction: the equation of the forces is
(1)
where
R is the normal reaction of the floor (upward)
is the component of the force F in the vertical direction (downward)
mg is the weight of the crate (downward)
- Horizontal direction: the equation of the forces is
(2)
where
is the horizontal component of the force F (forward)
is the force of friction (backward)
From (1) we get
And substituting into (2)
b)
In this second case, the crate is still at rest, so we have to consider the static force of friction, not the kinetic one.
The equations of the forces will be:
(1)
(2)
In this second case, we want to find the critical value of such that the woman cannot start the crate: this means that the force of friction must be at least equal to the component of the force pushing on the horizontal direction,
.
Therefore, using the same procedure as before,
And solving for ,
Now we analyze the expression that we found. We notice that if the force applied F is very large, , therefore we can rewrite the expression as
So, this is the critical value of the coefficient of static friction.
Answer:
Case 1: <u>Pushing</u> Diagram 1
Leaning over and Pushing the heavy box from the floor, the push will be divided in to two parts, one is horizontal that can help the box move, and one is vertically downwards, which increases the downward force of the heavy object (an addition to the gravity) and thus increases friction, making it very hard to push. When you push at certain angle, you are exhibiting two forces as shown in diagram 1.
- Horizontal force acting along the plane.
- Vertical force downward perpendicular to the surface.
Case 2: <u>Pulling</u> Diagram 2
Pulling on a rope similar object at the same angle, the pull can be divided into two parts, one is horizontal that can help the box move, and one is vertically upwards, which decreases the downwards force of the box (a subtraction in the gravity) and thus decreases friction, making it very easy to pull. When you pull at a certain angle, you are exhibiting two forces as shown in diagram 2.
- Horizontal force acting along the plane.
- Vertical force upward perpendicular to the surface.
So, in the case of pushing, it adds an extra weight on the object, which results in difficulty to push that object at the same angle. In case of pulling, the upward perpendicular force, it tries to lift the object upward and divided the weight partially. Thus making it easier to move the object at same angle.
