F=K*X,
F=M*a 
M*a=K*X
2.5*9.81=K*0.0276
24.525=K*0.0276
24.525/0.0276=K
K= 888.6 N/m ---- force constant 
assuming 2.5 refers to the new extension, just divide F/ 0.025
to get
981N/m 
        
             
        
        
        
Answer:
4km
Explanation:
15 minutes is 1/4 of an hour.
1/4 of 16 is 4.
 
        
             
        
        
        
6.  Since we are not sure if the person in the question is actively lifting the crate, we have to determine the downwards force of the crate due to gravity and compare it to the normal force.  
F = ma
F = (15.3)(-9.8)
F = -150N
Since the downwards force of the crate is equivalent to the normal force, it means the person is applying no force in picking up the object.  So to pick up a 150N object from scratch, you would have to exert more force than the weight of the object, so the answer is 294N.
7.  Same idea as question 2.  
First determine the weight of the object:
F = ma
F = (30)(-9.8)
F = -294N
The crate in question is not moving, so the magnitudes of the forces in the upwards and downwards direction has to equal to 0.
-294 + 150N + x = 0
x = 144N  
So the person is exerting 144 N.
10.  First find the force of block B to the right due to its acceleration:
F = ma
F = (24)(0.5)
F = 12N
So block B is moving 12N to the right relative to block A due to block A's movement to the left.  However, block A is being applied a much greater force and is moving quicker to the left than block B is moving to the right of bock A.  The force that is causing block B to experience the lower relative force to the right is because of the friction.  To find the friction:
The sum of the forces in the leftward and rightward direction for block B must equal 12N.
75 - x = 12
x = 63N
So the force of friction of block A on block B is 63N to the left.
 
        
             
        
        
        
Answer and Explanation:
The computation of the shortest wavelength in the series is shown below:-

Where
 represents wavelength
 represents wavelength
R represents Rydberg's constant
 represents Final energy states
 represents Final energy states
and  represents initial energy states
 represents initial energy states
Now Substitute is

now we will put the values into the above formula


Now we will rewrite the answer in the term of 

So, the whole Paschen series is in the part of the spectrum.
 
        
             
        
        
        
Answer:
Explanation:
First of all, I used the specific heat of water as 4182 J/(kgC) and the specific heat of ethyl alcohol (EtOH) as 2440 J/(kgC); that means that we need the masses in kg, not g.
120.g = .1200 kg of ethyl alcohol. Now for the formula:
 where spheat is specific heat.
 where spheat is specific heat.
Filling that horrifying-looking formula in with some values:
 and
 and
 and
 and
16(4182x + 292.8) = 83640x + 2928 and
66912x + 4684.8 = 83640x + 2928 and
1756.8 = 16728x so
x = .105 kg and the amount of water added is 105 g