## May 18, 2020

### KINEMATICS - 3 (MASTER ADVANCED PHYSICS)

KINEMATICS - 3 (MASTER ADVANCED PHYSICS)
(For all Top Exams)

Video – 3
KINEMATICS - 3

Motion under Gravity

We must remember that even in straight line motion, we have positive and negative directions for velocity, acceleration and displacement

a=g = 9.8 m/s/s

1. Body dropped from a height – h

Equations

U= 0, v= v, S= H, t= t (time of flight)

a= +g

So, V= g*t

H= ½ gt2

v2= 2*g*H

Time of fall = t = root of 2h/g

Velocity with which it reaches the ground = v= root of 2gh

2. When a body is thrown upwards with a velocity – u

Equations – upwards – positive , downwards – negative

U= u, v= 0 , a= -g, s= H, t= t

0= u-gt

h = ut – ½ gt2

U2 = 2*g*h

So,

Maximum height reached = h= u2/2g

Time of ascent= time of descent = u/g

Total time in flight = 2u/g

3. Body projected from a tower of height H with velocity – u

Equations – upward is positive

Downward is negative

U= u, s= -h(height of the tower is displacement) , t= t , v= -v, g= g

U2- V2= -2gh

So,

Velocity with which it reaches the ground = v = root of u2 +2gh

Total time taken to reach the foot of tower = time to reach the top + time of fall

= u/g + root of (u2 +2gh) / g