Answer:
k = 49 N/m
Explanation:
Given that,
Mass, m = 250 g = 0.25 kg
When the mass is attached to the end of the spring, it elongates 5 cm or 0.05 m. We need to find the spring constant. Let it is k.
The force due to mass is balanced by its weight as follows :
mg=kx

So, the spring constant of the spring is 49 N/m.
 
        
             
        
        
        
Answer:
No, there won't be a collision.
Explanation:
We will use the constant acceleration formulas to calculate,
v = u + a*t
0 = 25 + (-0.1)*t
t = 250 seconds (the time taken for the passenger train to stop)
v^2 = u^2 + 2*a*s
0 = (25)^2  + 2*(-0.1)*s
s = 3125 m (distance traveled by passenger train to stop)
If the distance traveled by freight train in 250 seconds is less than (3125-200=2925 m) than the collision will occur
Speed*time = distance
Distance = (15)*(250)
Distance = 3750 m
As the distance is way more, there won’t be a collision
 
        
             
        
        
        
Explanation:
1. Convex mirror is curved outward.
2. Convex mirror forms an image that is smaller than the object.
3. Concave mirror is used to focus light rays. That's why it is also known as a converging mirror. 
4. Plane mirror has a flat surface. It forms the same size of the image as that of the object.
 
        
                    
             
        
        
        
-- Put the rod into the freezer for a while.  As it cools, 
it contracts (gets smaller) slightly.
-- Put the cylinder into hot hot water for a while.  As it heats,
it expands (gets bigger) slightly.
-- Bring the rod and the cylinder togther quickly, before the 
rod has a chance to warm up or the cylinder has a chance 
to cool off.
-- I bet it'll fit now.
-- But be careful . . . get the rod exactly where you want it as fast
as you can.  Once both pieces come back to the same temperature,
and the rod expands a little and the cylinder contracts a little, the fit
will be so tight that you'll probably never get them apart again, or even
move the rod.