Answer:
When the polythene rod is rubbed with the woolen cloth, static electric charges move from the cloth and into the rod. The rod becomes negatively charged as negative charges move from the cloth and into the rod leaving the cloth positively charged as well.
 
        
             
        
        
        
t  = 0.527 s
<u>It accelerates for 0.527 s.</u>
<u>Explanation:</u>
We use the formula: 
 v = u+at
 Given:
 v = 106 m/s
 u = 0 (since no gravity)
 
 So applying the formula,
 v = u+at
106 = 0 + 201t
 t     = 106/201
 t     = 0.527 s
 
        
             
        
        
        
Answer:
19.95 J
Explanation:
The center of mass of the ladder is initially at a height of:

The center of mass of the ladder ends at a height of:
 =L/2
So, the work done is equal to the change in potential energy which is:
W = PE = 
now 
therefore
W = [mgL/2]×[1 - sin(theta)]
W = [(7.30)(9.81)(2.50)/2]×[1-sin(51°)]
solving this we get 
W = 19.95 J 
 
        
             
        
        
        
If 56.5kJ are needed to raise the temp by 90°C and if the heater is 60% efficient that means that:
60% X y = 56.5kJ
where y is the electrical energy in kJ that the heater will use.
y = 94.2kJ