When a student combed his dry hair for a long time, his hair began to stand up. which of these has most likely happend?

B)The comb and hair have become charged with opposite charges.

Explanation:

When the comb was rubbed against dry hair, electrons moved from the hair to the comb. While the hair became positively charged, the comb became negatively charged by acquiring an excess static charge. In other words, the comb and hair have become charged with opposite charges.

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s