Answer:
v=18.54167 m/s
Explanation:
the law of linear momentum conservation says that when the resultant force in an object is null, the linear momentum is constant over time, so in accordance the paragrapfh the railroad car is moving and the forces acting on it is the weight and the normal force, so we can say that the resultant force on the railroad car are equal to zero
So, the linear momentum can be written

V_{1}= 15m/s
m1= 89000 kg
To the m2 we subtract the weight of sand that leak out
m2= 89000 kg - 17000 kg =72 000 kg
V_{2}=
V_{2}= 18.54167 m/s
Explanation:
For 787 dreamliner airplane,
Mass, 
Height, 
Potential energy of 787 dreamliner airplane is given by :

For a boeing 747,
Mass, 
Height, 
:
Potential energy of a boeing 747 airplane is given by

So, the potential energy of a boeing 747 airplane is more than the 787 dreamliner airplane.
The natural process is called greenhouse effect. This is when the Sun's light enters the Earth, and converts to heat. Light passes through the Earth's atmosphere much easier compared to heat. Because of this, heat is trapped on Earth because it cannot exit the atmosphere as easily as light does.
Total distance travelled by the car is 'd'
<span>distance trveled before the brakes were applied = v_o * t </span>
<span>distance travld with brakes = d - v_o*t </span>
<span>applying the formula: v^2 - u^2 = -2 a * s </span>
<span>=> 0 - v_o^2 = -2 * a_x * (d- v_o*t) </span>
<span>=> a_x = (v_o^2)/ ( 2 (d-v_o*t)</span>
You could increase the mechanical efficiency of this screw by reducing friction along the screw threads