A material point, moving uniformly accelerated in a straight line in one direction, during time

A material point, moving uniformly accelerated in a straight line in one direction, during time t increased its speed 3 times, having traveled a path of 20 m. Find t if the acceleration of the point is 5 m / s².

Given:

S = 20 meters – the distance covered by the material point in time t;

a = 5 m / s ^ 2 – point acceleration;

v1 = 3 * v0 – the point has increased its speed 3 times in time t.

It is required to determine the time of movement of the point t.

Let’s find the initial speed of the body:

(v1 – v0) / a = t;

(3 * v0 – v0) / a = t;

2 * v0 / a = t.

S = v0 * t + a * t ^ 2/2 = v0 * 2 * v0 / a + a * 4 * v0 ^ 2 / (2 * a ^ 2) =

= 2 * v0 ^ 2 / a + 2 * v0 ^ 2 / a = 4 * v0 ^ 2 / a, hence:

v0 = (a * S / 4) ^ 0.5 = (5 * 20/4) ^ 0.5 = (5 * 5) ^ 0.5 = 25 ^ 0.5 = 5 m / s.

Then the time of movement of the body is equal to:

t = 2 * v0 / a = 2 * 5/5 = 2 seconds.

Answer: the time of body movement is 2 seconds.