The correct answer is
C. reduce the friction between its moving parts
In fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.
The force required is 319 N
Explanation:
The force of static friction is a force that acts an object on a surface, when this object is pushed by another force to put it in motion. The direction of the force of friction is opposite to the direction of the force of push, and its value increases as the force of push increases, up to a maximum value given by:
where
is the coefficient of friction
W is the weight of the object
Therefore, in order to put the object in motion, the force applied must be greater than this value.
For the pile of leaves in this problem, we have:
(coefficient of friction)
(weight of the leaves)
Substituting, we find:
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Answer:
Approximately (approximately ) assuming that the magnetic field and the wire are both horizontal.
Explanation:
Let denote the angle between the wire and the magnetic field.
Let denote the magnitude of the magnetic field.
Let denote the length of the wire.
Let denote the current in this wire.
The magnetic force on the wire would be:
.
Because of the term, the magnetic force on the wire is maximized when the wire is perpendicular to the magnetic field (such that the angle between them is .)
In this question:
- (or, equivalently, radians, if the calculator is in radian mode.)
- .
- .
- .
Rearrange the equation to find an expression for , the current in this wire.
.
The law of reflection states that when a ray of light reflects off a surface, the <em>angle of incidence is equal to the angle of reflection</em>.
In this question, the light ray passes from air to water, an optically denser medium.
Imagine drawing a line to representing the boundary between two mediums. Now imagine drawing a line perpendicular to that boundary line marking where the light ray intersects the boundary line. This second line is called the normal. Whenever a light ray passes into a denser medium with a nonzero angle of incidence, the ray will bend towards the normal, making the <em>angle of refraction smaller than the angle of incidence</em>.
Choice A