Using calculus prove the relation between distance, time, speed and acceleration

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neela | High School Teacher | (Level 3) Valedictorian

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We presume s(t) = A+Bt+Ct^2 , where s is the distance travelled by a particle in time t with a starting velocity u and final velocity v and acceleration a.

To find the relation between  s,a,u and v.

At time 0, t= 0.

s(0) = A+B*0+C*0^2 = 0. So, A =0.

Differentiate both sides of s(t) = A+Bt+Ct^2 , with respect to time variable t, we get:

s'(t) = B +2Ct. So when t = 0,  s'(0) = B+2C*0 = u. So  B  = u.

s"(t) = (B+2Ct)' = (B)' +(2Ct)' = 0+2C. So 2C = acceleration a.

So, C = a/2.

Replacing the values for A= 0, B = u and C = a/2 in the pressumed equation , s(t) = A+BT+Ct^2 , we get:

s(t) = ut+(1/2)at^2...........(1).

Also B = u and velocity after time t is v = B+2Ct or

v = u +2(a/2)t

v = u+at..............................(2)

So equations (1) and (2) established the relation between the distance , initial velocity, final velocity, acceleration and time.

Also s(t) = ut+(1/2)(at^2). Substitute for t from u+at = v or t = (v-u)/a .

s(t) = u(v-u)/a + (1/2)a[(v-u)/a]^2

s(t) = uv/a -u^2/a + v^2/2a - uv/a + u^2/2a

s(t) = (v^2 = u^2)/2a.


2as(t) = v^2-u^2  is a relation bweteen  distance travelled s(t) , initial velocity vu and final velocity v.



william1941's profile pic

william1941 | College Teacher | (Level 3) Valedictorian

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Let the distance travelled by a body be only a function of time or we can represent the distance as d = f(t).

Now speed is the distance travelled in a unit time. The  instantaneous speed is the derivative of the function that represents distance.

Or the speed, s(t) = f'(t)

Acceleration is the change in speed divide by the time taken. The instantaneous acceleration is the derivative of the function representing speed or s'(t).

As s(t) = f’(t), acceleration can also be represented as the second derivative of the function representing distance travelled or f''(t).