Answer: 0.392 m/s
Explanation:
The Doppler shift equation is:

Where:
 is the actual frequency of the sound wave
 is the actual frequency of the sound wave
 is the "observed" frequency
 is the "observed" frequency
 is the speed of sound
 is the speed of sound
 is the velocity of the observer, which is stationary
 is the velocity of the observer, which is stationary
 is the velocity of the source, which are the red blood cells
 is the velocity of the source, which are the red blood cells
Isolating  :
:


Finally:

 
        
             
        
        
        
Answer: D
The final velocity of the object will be directed north of east
Explanation:
 
        
                    
             
        
        
        
I think you're saying that once you start pushing on the cars, you want to be able to stop each one in the same time.  
This is sneaky.  At first, I thought it must be both 'c' and 'd'.  But it's not 
kinetic energy, for reasons I'm not ambitious enough to go into.
(And besides, there's no great honor awarded around here for explaining 
why any given choice is NOT the answer.) 
The answer is momentum.
Momentum is (mass x speed).  Change in momentum is (force x time).
No matter the weight (mass) or speed of the car, the one with the greater 
momentum is always the one that will require the greater (force x time)
to stop it.  If the time is the same for any car, then more momentum
will always require more force.
        
             
        
        
        
Answer:
Reduce the friction at the surface
Explanation:
If you can reduce the friction between the load and the plane less effort will be required as you are not having to apply effort to overcome friction.