Answer: Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact
 
        
             
        
        
        
Answer:
 Option D. ²³⁹₉₃Np
Explanation:
Let the unknown be ʸₓA. 
Thus, the equation becomes:
²³⁹₉₂U —> ⁰₋₁e + ʸₓA
Next, we shall determine the x, y and A. This can be obtained as follow:
92 = –1 + x
Collect like terms 
92 + 1 = x
93 = x
x = 93
239 = 0 + y
239 = y
y = 239
ʸₓA => ²³⁹₉₃A => ²³⁹₉₃Np
Thus, the complete equation is:
²³⁹₉₂U —> ⁰₋₁e + ²³⁹₉₃Np 
 
        
             
        
        
        
Answer:
The image distance is 20.0 cm.
Explanation:
Given that,
Power = 1.55 dp
Distance between book to eye = 26.0+3.00=29.0 cm 
We need to calculate the focal length
Using formula of focal length

Put the value into the formula



We need to calculate the image distance
Using lens formula


Put the value into the formula



Hence, The image distance is 20.0 cm.
 
        
             
        
        
        
Answer:
The magnification of an astronomical telescope is -30.83.
Explanation:
The expression for the magnification of an astronomical telescope is as follows;

Here, M is the magnification of an astronomical telescope,  is the focal length of the eyepiece lens and
 is the focal length of the eyepiece lens and  is the focal length of the objective lens.
 is the focal length of the objective lens.
It is given in the problem that an astronomical telescope having a focal length of objective lens 74 cm and whose eyepiece has a focal length of 2.4 cm.
Put  and
 and  in the above expression.
 in the above expression.

M=-30.83
Therefore, the magnification of an astronomical telescope is -30.83.