Answer:
Volume charge density: When the charge density is throughout the volume of a body, then the charge per unit volume is called volume charge density and it is represented by ρ.
∴ρ=
Hence the unit of ρ is Cm
−3
Example: If a charge q is uniformly distributed in the whole volume of a
sphere of radius R, then p =
=3q/4πR-3
Work is done when a force is in the same direction as the object moves.
Explanation:
The work done by a force in moving an object is given by the equation
where
F is the magnitude of the force
d is the displacement of the object
is the angle between the directions of F and d
From the equation, we notice the following:
- Work is done by a force when the force is in the same direction as the object moves. In fact, in this case,
, and so 
, which means that the work done simply becomes 
- When the force is perpendicular to the motion of the object,
and 
, which means that no work done - Technically, work is also done when the force is not parallel to the motion of the object: in this case, the factor
means that only the component of the force parallel to the direction of motion contributes to do work on the object.
Therefore, the correct answer is
Work is done when a force is in the same direction as the object moves.
Learn more about work:
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You will always have mucus fluid, but if you are healthy it is thin. When your sinuses become enflamed the mucus becomes thick.
Answer:
True.
Explanation:
Newton's First Law of Motion states that every object continues in it's state of rest or of uniform motion in a straight line unless acted upon by an external force.
Answer:
Final speed of car = 12 m/s
Explanation:
We have equation of motion v = u + at, where v is final velocity, u is initial velocity, a is acceleration and t is time.
a) A cart starts from rest and accelerates at 4.0 m/s² for 5.0 s
v = ?
u = 0 m/s
a = 4.0 m/s²
t = 5 s
v = u + at = 0 + 4 x 5 = 20 m/s
b) Then maintains that velocity for 10 s
v = ?
u = 20 m/s
a = 0 m/s²
t = 10 s
v = u + at = 20 + 0 x 10 = 20 m/s
c) Then decelerates at the rate of 2.0 m/s² for 4.0 s
v = ?
u = 20 m/s
a = -2.0 m/s²
t = 4 s
v = u + at = 20 + -2 x 4 = 12 m/s
Final speed of car = 12 m/s
