Answer
given,
distance = 140 m
time, t = 3.6 s
moving speed = 53 m/s
a) distance = (average velocity) x time


v₀ + 53 = 77.78
v₀ = 24.78 m/s or 25 m/s
b) 

a = 7.8 m/s²
using equation of motion
v₀² = v₁² + 2 a s
53² = 0²+ 2 x 7.8 x s
s = 180 m
Care este problema? Btw why are you speaking Romanian
density is correct hope this helps
The force exerted on the box is 56 N
Explanation:
The work done by a force on an object is given by

where
F is the magnitude of the force
d is the displacement of the object
is the angle between the direction of the force and of the displacement
For the box in this problem, we have:
W = 2240 J is the work done
d = 40 m is the displacement of the box
Assuming that the force is parallel to the displacement, 
Solving the equation for F, we find the force exerted on the box:

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Answer:
Electrical force, F = 90 N
Explanation:
It is given that,
Charge on sphere 1, 
Charge on sphere 2, 
Distance between two spheres, d = 6 cm = 0.06 m
Let F is the electrical force between them. It is given by the formula of electric force which is directly proportional to the product of charges and inversely proportional to the square of distance between them such that,


F = 90 N
So, the electrical force between them is 90 N. Hence, this is the required solution.