Well, the thing is: we don't really know, as we don't even know how many species there are on earth. 
If we take a look at the estimates of <span>World Wide Fund for Nature, an organization that works toward combating species extinction, their estimates vary from 200 to 100 000 - but a probable number is 20 000 (d). </span>
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You can tell a lot about an object that's not moving,
and also a lot about the forces acting on it:
==> If the box is at rest on the table, then it is not accelerating.
==> Since it is not accelerating, I can say that the forces on it are balanced.
==> That means that the sum of all forces acting on the box is zero, 
and the effect of all the forces acting on it is the same as if there were
no forces acting on it at all.
==> This in turn means that all of the horizontal forces are balanced,
AND all of the vertical forces are balanced.
Horizontal forces: 
sliding friction, somebody pushing the box
All of the forces on this list must add up to zero. So ...
(sliding friction force) = (pushing force), in the opposite direction.
If nobody pushing the box, then sliding friction force = zero.
Vertical forces:
gravitational force (weight of the box, pulling it down)
normal force (table pushing the box up)
All of the forces on this list must add up to zero, so ...
(Gravitational force down) + (normal force up) = zero
(Gravitational force down) = -(normal force up) .
        
                    
             
        
        
        
Three 40w lamp for 6 hours
        
             
        
        
        
The rays of light coming from the Sun are parallel to each other, so when they are reflected by the concave piece of glass (which acts as a concave mirror) they converge into the focus of the mirror, which is

The radius of curvature of a concave mirror is twice its focal length, so in this case it is:
 
 
        
        
        
Answer:
(a) I=0.01 kg.m²
(b) I=0.03 kg.m²
Explanation:
Given data
Mass of disk M=2.0 kg
Diameter of disk d=20 cm=0.20 m
To Find
(a) Moment of inertia through the center of disk
(b) Moment of inertia through the edge of disk
Solution
For (a) Moment of inertia through the center of disk
Using the equation of moment  of Inertia

For (b) Moment of inertia through the edge of disk
We can apply parallel axis theorem for calculating moment of inertia
