Answer:
a)
b)
c)
Explanation:
We use the definition of a electric field produced by a point charge:

<u>a)Electric Field due to the alpha particle:</u>

<u>b)Electric Field due to electron:</u>

<u>c)Electric Force on the alpha particle, on the electron:</u>
The alpha particle and electron feel the same force but with opposite direction:

Answer:
4 seconds
Explanation:
There are links between cars, they are in between
1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17.
Here 1 represents the first car which is firmly attached to the engine. So, there are 16 links and each link has a slack of 9 m.
So, total slack
9×16 = 144 cm
Speed of train = 36 cm/s

Time taken by the pulse to travel the length of train is 4 seconds.
Iodine-131 has a half life of 8 days, so half of it is gone every 8 days.
10 grams of iodine-131 is left for 24 days.
At 8 days: 10/2=5 grams left
At 16 days: 5/2=2.5 grams left
At 24 days: 2.5/2=1.25 grams left.
**
Your mistake is that you stopped at 16 days.