the answer choice will be A because they travel at the same speed through only light not one material.
 
        
                    
             
        
        
        
Answer:
25 mm = 0 deg C
200 mm = 100 deg C
200 - 25 = 175 = change in thread per 100 deg C
95 - 25 = 70 mm - change in thread from 0 deg C
70 / 175 * 100 = 40 deg C    final temperature at 95 mm
 
        
             
        
        
        
m = mass of the box 
N = normal force on the box 
f = kinetic frictional force on the box 
a = acceleration of the box
μ = coefficient of kinetic friction 
perpendicular to incline , force equation is given as 
N = mg Cos30                                         eq-1
kinetic frictional force is given as 
f = μ N
using eq-1
f = μ mg Cos30    
parallel to incline , force equation is given as 
mg Sin30 - f = ma 
mg Sin30 - μ mg Cos30  = ma 
"m" cancel out
a = g Sin30 - μ g Cos30
inserting the values
1.20 = (9.8) Sin30 - (9.8) Cos30 μ
μ = 0.44 
 
        
             
        
        
        
If the velocity of the chair is constant, then the net force acting on it is zero.
The force you exert to keep it going is equal and opposite to the force of friction.