The time when both the balls meet is found to be 8.4seconds.
By Newton’s third equation of motion
h = ut -1/2 gt²
-(210-h) = ½ ×gt²
h= 210 -1/2 gt² (eq.1)
Now, we apply same equation for the ball thrown upward with initial speed of 25m/s
h = ut -1/2 gt²
h = 25t -1/2gt² (eq.2)
On comparing eq. 1 and eq. 2 we get,
210 -1/2gt² = 25t -1/2gt²
210 = 25t
t = 8.4 sec.
Thus, the time when both the balls meet is found to be 8.4sec.
There are three laws of motion, which are stated by Sir, Isaac Newton. He describes the relation between the motion of the object and the forces which are acting on it during a projectile or simple motion. On the basis of three laws of motion, equations are dervied which are used to find the speed, height, velocity or acceleration of the object.
The three equations of motions are as follows:-
1. V= u + at
2. S= ut +1/2 at²
3. v²=u² + 2as.
Where, v is the final velocity, u is initial velocity, a is acceleration, s is distance covered and t is time taken.
To learn more about laws of motion, refer this link
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