Answer:
v = 0.92 c
Explanation:
Here, we will use the time dilation formula from Einstein's theory of relativity to find the speed of traveling of the friend:

where,
v = speed of traveling = ?
c = speed of light
t = time of return = 10 years
t₀ = time passed on earth = 4 years
Therefore,

<u>v = 0.92 c</u>
It was Niels Bohr who proposed it
Answer:
a) X = 17.64 m
b) X = 17.64 + 4∆t^2 + 16.8∆t
c) Velocity = lim(∆t→0)〖∆X/∆t〗 = 16.8 m/s
Explanation:
a) The position at t = 2.10s is:
X = 4t^2
X = 4(2.10)^2
X = 17.64 m
b) The position at t = 2.10 + ∆t s will be:
X = 4(2.10 + ∆t)^2
X = 17.64 + 4∆t^2 + 16.8∆t m
c) ∆X is the difference between position at t = 2.10s and t = 2.10 + ∆t so,
∆X= 4∆t^2 + 16.8∆t
Divide by ∆t on both sides:
∆X/∆t = 4∆t + 16.8
Taking the limit as ∆t approaches to zero we get:
Velocity =lim(∆t→0)〖∆X/∆t〗 = 4(0) + 16.8
Velocity = 16.8 m/s
charge = current x time = 0.5x 20=10Coulombs