3.33 seconds.
<u>Explanation:</u>
We can find the speed of the body using the formula, 
Speed = Distance traveled in meters /  time taken in seconds
= 450 m / 30 seconds
= 15 m/s 
So per second the distance traveled by the body is 15 m.
So time needed to travel 50 m can be found as, 
time = distance/speed
= 50 m / 15 m /s
= 3.33 s
 
        
             
        
        
        
It's actually Friction.
I just did the test and got it right.
 
        
                    
             
        
        
        
Answer: find the answer in the explanation 
Explanation:
When a magnet is placed at the centre of the paper, and the nails are sprinkled on the paper, what will happen to the nails is that, the nails will form a pattern on the paper according to the magnetic field of the bar magnetic pole.
Other phenomena you can observe are:
1.) The nails will align themselves and show some lines of forces which is equivalent to the magnetic field lines 
2.) The direction of the line of forces
3.) The strength of the magnetic field pole.
 
        
             
        
        
        
The kinetic energy would be 53,775J:)