Difference between 2nd and 3rd equation of motion
2nd equation of motion
1.) Second equation of motion gives the relation between initial velocity, displacement and acceleration of object.
2.) Using graphical method, 2nd equation of motion is derived as,
∴ s = ut + 1/2 at2
Where, u = initial velocity
s =displacement
a = acceleration
t = time.
3.) Second equation is very useful in finding the displacement, acceleration, initial velocity and time.
4.) Eg. Batsman hits the ball towards boundary at speed of 30 m/s and uniform acceleration of 1.2 m/s2 takes 1.6 seconds cross the boundary rope. What is the distance of boundary from the batting crease?
Ans: u = 30 m/s, t = 1.6 sec, a = 1.2 m/s2
Using second equation of motion, we have
∴ s =ut + 1/2 at2
∴s = 20 × 2 + ½ × 1.2 × 1.62
∴ s = 60 + 0.6 × 2.56 = 92.16 m
3rd equation of motion
1.) Third equation of motion relates the initial velocity, final velocity, acceleration and displacement.
2.) Using graphical method, 3rd equation of motion is derived as,
∴ v2 = u2 + 2as
Where, u = initial velocity
v = final velocity
s =displacement
a = acceleration
3.) Third equation is very useful in finding the displacement, acceleration, initial velocity and final velocity.
4.) Eg. Bike running at speed of 60 km/h needs to apply instant brakes to stop. Before stopping bike covers distance of 12 m. What the retardation of bike is before comes to rest?
Ans: Here, u= 60 km/hr =60×(5/18)= 50/3 m/s
v = 0 m/s
s = 12 m
From 3rd equation of motion,