Answer:
Position =
behind the mirror
Nature = Virtual and Erect
Size =
: Diminished
Explanation:
Sign convention-Distance measured to the left of pole is negative and to the right of pole is positive.
Object distance = u = -20 cm
Focal length = f = Radius of curvature/2 = 30/2 = 15 cm
We have to use mirror formula to find image distance.

Since the image distance is positive, it is formed behind the mirror or a virtual image is formed.
Magnification = 

Height of the object = 5 cm
Height of the image = 
Since the height of the image is positive and less than the size of object,it is erect and diminished.
Answer:
We cannot place three forces of 5g, 6g, and 12g in equilibrium.
Explanation:
Equilibrium means their sum must be zero.
Here the forces are 5g, 6g, and 12g.
For number of forces to be in equilibrium the magnitude of largest vector should be less than sum of the magnitude of other vectors.
Here
Magnitude of largest force = 12 g
Sum of magnitudes of other forces = 5g + 6g = 11g
Magnitude of largest force > Sum of magnitudes of other forces
So this forces cannot form equilibrium.
We cannot place three forces of 5g, 6g, and 12g in equilibrium.