Answer:
w=255
Explanation:
The change in internal energy is given by the first law:
ΔE = Q - w
where ΔE is the change in internal energy of the system
q is the heat added to the system
w is the work done *by* the system on the surroundings
So, for the first phase of this process:
ΔE = Q - w
Q=160J
w=309J
ΔE = 160J - 309J = -149J
To bring the system back to its initial state after this, the internal energy must change by +149J (the system myst gain back the 149 J of energy it lost). We are told that the system loses 106 J of heat in returning to its initial state, so the work involved is given by:
ΔE = Q - w
+149J = -106J - w
255J = -w
w = -255J
Initial velocity(u)= 50m/s. t=2s. a= -9.8m/s². ( minus because acceleration is in downward direction). v=u+at. v= 50 - 9.8×2. v= 30.4m/s.
Answer is D.
Speed:
Use relative speed to simplify the situation. Since the trains are moving in opposite directions, you can add the speeds and pretend the first train is stationary (moving at 0m/s) and the second train is moving at 50m/s.
Distance:
The front of the second train needs to travel 120m to get from the front to the back of the first train. When the front of the second train is at the back of the first train, the back of the second train is still 10m in front of the first train. The back therefore has to travel 130m to clear the first train. The total distance over which the trains are overlapping in this scenario is therefore 120 + 130 = 250m.
You have speed and you have distance so now just calculate time:
v = d / t
50 = 250 / t
t = 5s