Answer: 
The chromium nucleus will complete the reaction.
Explanation:
The given reaction is a type of radioactive nuclei decay:
Positron emission: It is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. This is also known as
-decay. In this the mass number remains same.

Now according to the given reaction:

The chromium nucleus will complete the reaction.
I see the light moving exactly at speed equal to c.
In fact, the second postulate of special relativity states that:
"The speed of light in free space has the same value c<span> in all inertial frames of reference."
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The problem says that I am moving at speed 2/3 c, so my motion is a uniform motion (constant speed). This means I am in an inertial frame of reference, so the speed of light in this frame must be equal to c.
Momentum before the collision
x-direction:
p = m₁v₁ = 1.5 * 4.5 = 6.75
x-direction:
p = 0
momentum after the collision is conserved:
x-direction:
p = 6.75 = m₁v₁ + m₂v₂ = 1.5 * 2. 1* cos -30° + 3.2 * v₂*cos θ
y-direction:
p = 0 = m₁v₁ + m₂v₂ = 1.5 * 2.1 * sin -30° + 3.2 * v₂ * sin θ
Solve the two equations for v₂ and θ.
Answer:

Explanation:
Given that,
Initial speed, u = 5 m/s
Final speed, v = 10 m/s
Time, t = 2 s
The radius of the tire of the bike, r = 35 cm
We need to find the angular acceleration of the pebble during those two seconds. It can be calculated as follows.

So, the required angular acceleration of the pebble is equal to
.
If you don't wear a helmet and let's say you fell off your bike, you can severely injure your head! But if you DO wear a helmet and you fell off your bike, there's about I predict a 98% chance that you won't injure but sometimes it's 100%
hope this helps!<span />