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