Explanation:
The compass needle moved when the wire was connected to the battery. The important point here is that the needle is affected by the wire only when both ends of the wire are connected to the battery because only at this time is current flowing through the circuit.
The correct answer is: acceleration.
In fact, the slope of the graph of velocity versus time corresponds to the ratio between the variation of v and the variation of t:

But this is exactly the definition of acceleration:

, so acceleration is the correct answer.
Answer:
a) 16.46 seconds.
b) 13.46 seconds
c) 2.67 m/s²
Explanation:
Acceleration = a = 1.35 m/s²
Final velocity = v = 80 km/h = 
Initial velocity = u = 0
Equation of motion

Time taken to accelerate to top speed is 16.46 seconds.
Acceleration = a = -1.65 m/s²
Initial velocity = u = 80 km/h= 
Final velocity = v = 0

Time taken to stop the train from top speed is 13.46 seconds
Initial velocity = u = 80 km/h= 
Time taken = t = 8.3 s
Final velocity = v = 0

Emergency deceleration is 2.67 m/s²
Answer:
μs = 0.75
μk = 0.58
Explanation:
From a force diagram:
(1)
(2)
When it starts slipping, friction force is the maximum and acceleration is 0. Replacing these conditions on (1):
Solving for μs:

μs = tan 36.7° = 0.75
When it moves at constant speed, friction force is kinetic friction and acceleration is 0. With these conditions the coefficient is:
μk = tan 30.1° = 0.58