Given data:
Mass of the body (m) = 4 kg
Distance traveled in the first second (d1) = 5 m
Distance traveled in the third second (d3) = 2 m

Calculating acceleration:
We know that distance traveled in the first second is given by the equation:
d1 = u + (1/2)at^2
where u is the initial velocity and t is the time taken.
Since the body starts from rest, the initial velocity (u) is zero.
Therefore, we can rearrange the equation as:
a = 2d1/t^2

Substituting the given values, we get:
a = 2 * 5 / 1^2 = 10 m/s^2

Calculating force:
We know that force (F) is given by the equation:
F = ma
where m is the mass of the body and a is the acceleration.

Substituting the given values, we get:
F = 4 kg * 10 m/s^2 = 40 N

Therefore, the force acting on the body is 40 Newtons.

Explanation:
- To calculate the force acting on the body, we first need to determine the acceleration. This can be done using the equation for distance traveled in the first second.
- By substituting the values of distance and time, we can find the acceleration.
- Once we have the acceleration, we can use the equation for force to calculate the force acting on the body.
- The force is determined by multiplying the mass of the body with the acceleration.
- In this case, the mass of the body is given as 4 kg, and the acceleration is found to be 10 m/s^2.
- By substituting these values, we find that the force acting on the body is 40 Newtons.

Key points:
- Mass of the body (m) = 4 kg
- Distance traveled in the first second (d1) = 5 m
- Distance traveled in the third second (d3) = 2 m
- Acceleration (a) = 10 m/s^2
- Force (F) = 40 N