Solution :
From the given data,
For the spherical shell is 
where x is the radius of gyration and the acceleration of a rolling body on an inclined plane = a
Therefore,



= 0.6 x 9.81 x sin ( 29.7)




Δt = 1.411 s
B) lever and pulley is the answer
Answer: Brownion motion is the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium.
Explanation:
Brownian motion is the random movement of particles in a fluid due to their collisions with other atoms or molecules.
Let the mass of 2500 kg car be
and it's velocity be
and the mass of 1500 kg car be
and it's velocity be
.
After the bumping the mass be M and it's velocity be V.
By law of conservation of momentum we have

2500 * 5 + 1500 * 1=4000 * V
V = 14000/4000 = 7/2 = 3.5 m/s
So the velocity of the two-car train = 3.5 m/s