Question

can you please explain me how these two highlighted equations are true for upward and downward motion? and how u is different in both case​

Answer 1

Answer:

Lemme explain in simple words...

for h = displacement

u = initial velocity

v = final velocity

g = acceleration due to gravity

t = time

Both the equations are the second equation of motion.

I guess u know about acceleration and deceleration.

well if so ..then , when we are falling (downward motion) , we r actually accelerating because of the increasing attracting force of the earth hence the g is (+) and hence the equation h = ut+½gt²

now when we decelerate (d), it's the opposite of acceleration(a) .

like a = (-d)

=> d = (-a)

so when we mean deceleration , we write it (-) acceleration.

now, when we throw something upwards, it's actually slowing down due to the regarding force of gravity ,pulling it in opposite direction with an

(deceleration) of 9.8 m/s² .

so deceleration = (-) acceleration

acceleration = (g)

substituting the vale of acceleration-

= (-) acceleration = (-g)

now the equation would be like...

ut + ½(-g)t²

= ut + (-½gt²)

= ut - ½gt² ( for upward motion)

Hope it helped :)