A pendulum is used in a large clock. The pendulum has a mass of 2 kg. If the pendulum is moving at a speed of 2.9 m/s when it re
2 answers:
This is a classic example of conservation of energy. Assuming that there are no losses due to friction with air we'll proceed by saying that the total energy mus be conserved.
Now having information on the speed at the lowest point we can say that the energy of the system at this point is purely kinetic:
Where m is the mass of the pendulum. Because of conservation of energy, the total energy at maximum height won't change, but at this point the energy will be purely potential energy instead.
This is the part where we exploit the Energy's conservation, I'm really insisting on this fact right here but it's very very important, The totam energy Em was
It hasn't changed! So inserting this into the equation relating the total energy at the highest point we'll have:
Solving for h gives us:
It doesn't depend on mass!
Now having information on the speed at the lowest point we can say that the energy of the system at this point is purely kinetic:
Where m is the mass of the pendulum. Because of conservation of energy, the total energy at maximum height won't change, but at this point the energy will be purely potential energy instead.
This is the part where we exploit the Energy's conservation, I'm really insisting on this fact right here but it's very very important, The totam energy Em was
It hasn't changed! So inserting this into the equation relating the total energy at the highest point we'll have:
Solving for h gives us:
It doesn't depend on mass!
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Friction:
Friction is the resistive force that acts on the body in a direction opposite to the direction of motion of the same object.
Laws of friction:
1. The frictional force acting on the object is proportional to the normal force acting on the object.
For example, if the object of mass m is moving along the horizontal surface, the normal force acting on the object is mg.
Thus, the frictional force acting on the object is,
where F_N is the normal force acting on the object,
The diagrammatic representation of the frictional force acting on the object is,
2. The frictional force acting on the object depends upon the nature of the surface in contact with the object.
3. The frictional force does not depend upon the area of contact of an object with the surface.
4. The kinetic friction acting on the object is independent of the velocity of the object.
5. The coefficient of static friction is more than the coefficient of kinetic friction.
Two factors on which the frictional force depends are:
1. The frictional force depends on the adhesion between the two bodies in contact.
2. The frictional force acting on the depends upon the roughness of the surface on which the object is moving.
Answer:
When viewed from above, the current in the coil should point towards the top-right corner of the picture.
Explanation:
The current in this coil have only two possible directions: clockwise or counter-clockwise. However, since the diagram shows the coil from above, not from a cross-section, just saying clockwise or counter-clockwise might be ambiguous. The statement that the current is directed towards the top-right corner of the picture is equivalent to saying that when viewed from the lower-right corner of this diagram, the current in the coil is moving clockwise.
Note that at the center of this picture, the current is parallel to the magnetic field- there will be no force on the coil at that position. On the other hand, (also when viewed from above,) at the top-right corner and the lower-left corner of the coil, the current in the coil will be perpendicular to the magnetic field. That's where the force on the coil will be the strongest.
With that in mind, apply the right-hand rule to find the direction of the force on the coil in each of the two possibilities.
Assume that when viewed from above, the current is flowing towards the top-right corner of the picture. Consider the wire near the top-right corner of this coil (as viewed above on this picture.) The current will be going into the picture into the magnetic field. By the right-hand rule, the current on the wire near that point should be pointing towards the bottom of this picture. (Point fingers on the right hand in the direction of the current . Rotate the right hand such that when curling the fingers, they point in the direction of the magnetic field
. The direction of the right thumb should now point in the direction of the force on the wire
.)
Based on the same assumption, the current in the wires near the bottom left corner of this coil will be pointing out of the picture. By the right hand rule, the magnetic force on the coil in that region should be pointing towards the top of this picture. Combing these two forces, the coil would indeed be rotating around the center of this picture in the direction shown in the diagram.
It can also be shown that if the current points towards the bottom left corner of the picture when viewed from above, the coil will be rotating about the center of this picture in the opposite direction.