Applying conservation of momentum;

Where m1 = 80.0 kg; v1 =4.10 m/s; m2 = 130.0 kg; v2 = 0; mf = (80+130) kg; vf = ??
Therefore,
80*4.1 + 130*0 = 210*vf
vf = (80*4.1)/210 = 1.56 m/s
Answer:
a) The astronauts would see the real length of the meter stick, i.e. L₀
b) The length of the meter stick as measured by the stationary observer will be 
Explanation:
a) Let the proper length of the meter stick be L₀
The meter stick and the astronauts on the on the space ship are on the same moving frame, therefore, they will see the exact length of the meter stick, that is, L₀
b) A stationary observer watching the space ship and meter stick travel past them will see a contracted length of the meter stick
The original length = L₀
Let the speed of the space ship = v
The contracted length, L, is related to the original length in the frame of rest by
L = L₀/γ......................(1)
Where γ =
....................(2)
Substituting equation (2) into (1)

So the question is asking for time.
Time= distance / speed
120/30
4
Therefore answer is d
To solve this problem we will apply the concept related to the electric field. The magnitude of each electric force with which a pair of determined charges at rest interacts has a relationship directly proportional to the product of the magnitude of both, but inversely proportional to the square of the segment that exists between them. Mathematically can be expressed as,

Here,
k = Coulomb's constant
V = Voltage
r = Distance
Replacing we have


Therefore the magnitude of the electric field is 