Answer:
x = 5.79 m
Explanation:
given,
mass of the car = 39000 Kg
spring constant = 5.7 x 10⁵ N/m
acceleration due to gravity = 9.8 m/s²
height of the track = 25 m
length of spring compressed = ?
using conservation of energy
potential energy is converted into spring energy




x = 5.79 m
the spring is compressed to x = 5.79 m to stop the car.
The magnitude of the source charge is 3 μC which generates 4286 N/C of the electric field. Option B is correct.
What does Gauss Law state?
It states that the electric flux across any closed surface is directly proportional to the net electric charge enclosed by the surface.

Where,
= electric force = 4286 N/C
= Coulomb constant = 
= charges = ?
= distance of separation = 2.5 m
Put the values in the formula,

Therefore, the magnitude of the source charge is 3 μC.
Learn more about Gauss's law:
brainly.com/question/1249602
The second one is correct not sure about the first one sorry
For Blake:
3 boxes at a distance of 10 meters each, each box weighs 20 N
Work done by Blake = 3 * 10m * 20N
= 600 J
Power = 600 J/ 2 min
= 300 J/min
For Sandra:
4 boxes, 15 N each at a distance of 12 meters each.
Work done by Sandra = 4 * 15 N *12m
= 720 J
Power = 720 J/ 4 min
= 180 J/min
Blake does less work than Sandra.
Blake's power is more than Sandra's.