Mass of yellow train, my = 100 kg
Initial Velocity of yellow train, = 8 m/s
mass of orange train = 200 kg
Initial Velocity of orange train = -1 m/s (since it moves opposite direction to the yellow train, we will put negative to show the opposite direction)
To calculate the initial momentum of both trains, we will use the principle of conservation of momentum which
The sum of initial momentum = the sum of final momentum
Since the question only wants the sum of initial momentum, 
(100)(8) + (200)(-1) = 600 m/s
        
             
        
        
        
Answer:
Explanation:
Magnitude of frictional force = μ mg 
μ is either static or kinetic friction. 
To start the crate moving , static friction is calculated .
a ) To start crate moving , force required = μ mg where μ is coefficient of static friction .
force required =.517 x 56.6  x 9.8 = 286.76  N . 
b ) to  slide the crate across the dock at a constant speed , force required 
= μ mg where μ is coefficient of kinetic  friction , where μ is kinetic friction 
= .26 x 56.6  x 9.8 = 144.21 N .
 
        
             
        
        
        
Answer:
The force is 274 N.
Explanation:
In figure 2:
(d) Let the tension in the string is T. 
According to the Newton's second law, 
Net force = mass x acceleration 
Apply for 200N. 

Now put in (1)
T - 114.7 = 20.4 x 7.81
T = 274 N 
 
        
             
        
        
        
Well potential energy is energy possessed by an object of by the position it's in. For example when you hold back a bow and arrow, but before you shoot it you are containing energy by holding the arrow back. So when you start the magnetic generator (pull or turn to start it) before using it for its purpose that is potential energy. I hope this helps.
 
        
             
        
        
        
My Answer: <span>If the electric field is zero everywhere inside a region of space, the potential must also be zero in that region.</span> If this is a true/false question, the correct answer would be false. 
Hope I helped! :D