Answer:
(a) 161.57 N
(b) 0.958 m/s^2
Explanation:
Force applied, F = 220 N 
mass of crate, m = 61 kg 
μ = 0.27 
(a) The magnitude of the frictional force, 
f = μ N 
where, N is the normal reaction 
N = m x g = 61 x 9.81 = 598.41 N 
So, the frictional force, f = 0.27 x 598.41 
f = 161.57 N 
(b) Let a be the acceleration of the crate. 
Fnet = F - f = 220 - 161.57 
Fnet = 58.43 N 
According to newton's second law 
Fnet = mass x acceleration 
58.43 = 61 x a 
a = 0.958 m/s^2 
Thus, the acceleration of the crate is 0.958 m/s^2.  
 
        
             
        
        
        
First, we need to convert the pressure in SI units. Keeping in mind that 

:

The initial and final volume of the gas are (keeping in mind that 

):


So, the work done on the gas by the surrounding is

And the final positive sign means that this work corresponds to an increase in internal energy of the gas.
 
        
        
        
Answer:
50 N
Explanation:
Since the refrigerator doesn’t move, that means the force of friction equals the amount of force the child exerts on the fridge. If the friction force were greater than the force by the child, the fridge would start accelerating towards the child. If it were less than the force the child exerted, the fridge would start accelerating away from the child. Therefore, the net force must be 0, in this case, the friction force is equal to the force the child exerted, for it to stay at rest (as Newton’s First Law stated). 
I hope this helps! :)