Physics questions (urgent)

1. The man's walking speed = d/60
where d is the length of the escalator
The speed of the escalator in bringing the man up = d/40

Hence, speed of man relative to ground when he stands on a moving escalator
= d/60 + d/40 = d/24
Time taken = d/(d/24) s = 24 s

2. After the ball is immersed in water, its apparent weight, as measured by spring balance B, becomes 1.5 N
Hence, upthrust acts on the ball by water = (2 - 1.5) N = 0.5 N

By Newton's 3rd Law (action and reaction), the same reaction acts on the water and which is recorded by balance A.
Therefore, reading on balance A = (6 + 0.5) N = 6.5 N

1. Time spent = 1/[ (1/40) + (1/60)] = 24 (s)

2. Its reading = 6 + 2 - 1.5 = 6.5 (N)

2014-12-17 23:17:28 補充：
In Q1, it is assumed that the man walks in the same direction as the escalator. However, if he walks in the opposite direction, the time spent will be 1 / [ (1/40) - (1/60) ] = 120 (s) instead of 24 (s).