Answer:
a. 30 N / m
b.  9.0 N
Explanation:
Given that
Unstretched length of the spring, 
 = 20.0cm = 0.2m
a) When the mass of 4.5N is hanging from the second spring, then extended length Is 
 = 35.0cm =  0.35m
So, the change in spring length when mass hangs is

= (0.35 - 0.20) m
= 0.15m 
As spring are identical 
Let us assume that the spring constant be "k", so at equilibrium
Restoring Force on spring = Block weightage
kx =  W =  4.50

= 30 N / m
b)  Now for the third spring, stretched the length of spring is 
 = 50cm = 0.5m
So, the change in spring length is 

= (0.5-0.20)m
=  0.30m
At equilibrium,
Restoring Force on spring = Block weightage
Now using all mentioned and computed values in above,

= 30(0.3)
= 9.0 N
 
        
             
        
        
        
Answer:
Potential difference though which the electron was accelerated is 
Explanation:
Given :
De Broglie wavelength , 
Plank's constant , 
Charge of electron , 
Mass of electron , m=9.11\times 10^{-31}\ kg.
We know , according to de broglie equation :

Now , we know potential energy applied on electron will be equal to its kinetic energy .
Therefore ,
 
Putting all values in above equation we get ,

Hence , this is the required solution.
 
 
        
             
        
        
        
Answer:
b) It is impossible to tell without knowing the masses.
Explanation:
The temperature change of a substance when it receives/gives off a certain amount of heat Q is given by

where
Q is the amount of heat
m is the mass of the substance
Cs is the specific heat capacity of the substance
In this case, we have a hot piece of aluminum in contact with a cold piece of copper: the amount of heat given off by the aluminum is equal to the amount of heat absorbed by the copper, so Q is the same for the two substances. However, we see that the temperature change of the two substances depends on two other factors: the mass, m, and the specific heat, Cs. So, since we know only the specific heat of the two substances, but not their mass, we can't tell which object will experience the greater temperature change.
 
        
             
        
        
        
Answer:
(a) v = 15m/a
(b) No they won't feast because the rock can only rise to a height of 11.5m which is less than 15m.
Explanation:
Please see the attachment below for film solution.
 
        
             
        
        
        
At the rear.
PWC stands for personal watercraft, and it is a small powerboat. The main components of a PWC are the hull (body of the boat), deck (surface where people walk/stand), throttle (controls speed), steering nozzle and water intake.