How many electrons (added or removed) are necessary to produce a charge of -4mc?

0.25 x 10^16 electrons

Explanation:

Given:

Q = -4 mC

Q = (-4 / 1000) C

Q = -0.004 C

To Find:

No. of electrons = ?

Solution:

Q = n x e

-0.004 = n x (-1.6) x 10^-19 C

-4 x 10^-3 x 10^19 / (-1.6) = n

10^16/4 = n

Therefore, n = 0.25 x 10^16 electrons

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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