When a man throws a ball vertically up his watch fall down from his hand.if the initial speep of the ball is 20m/s from a building.what will be its velocity when it reaches the ground if the height difference b/n them is 100m?

Someone will be glad to critique your thoughts.

Try using conservation of energy.

The business of his watch falling from his hand seems irrelevant. What does b/n mean?

Please work on your spelling, grammar and punctuation if you post here again.

tnx 4 ur coment but i post wat i had received frm ma frds.i was glad when i hear that 2 that's y i post it here.

To find the velocity of the ball when it reaches the ground, we need to use the concept of projectile motion.

First, let's assume that the negative direction is downward and the positive direction is upward.

We can use the equation of motion for vertical motion:

v = u + at

where:
- v is the final velocity (which we want to find)
- u is the initial velocity
- a is the acceleration
- t is the time

In this case, the initial velocity (u) of the ball is 20 m/s in the upward direction, and the acceleration (a) is equal to the acceleration due to gravity, which is approximately -9.8 m/s² (negative because it acts in the opposite direction to the motion).

Since the ball is thrown vertically upwards and then falls back to the ground, we can split the motion into two parts:

1. The upward motion of the ball:
Here, the final velocity (v) will be zero when the ball reaches its maximum height (at its peak). We can calculate the time taken to reach the peak using the equation:

v = u + at

0 = 20 - 9.8t

Solving this equation gives the time (t) it takes for the ball to reach its peak.

2. The downward motion of the ball:
Here, the initial velocity (u) will be zero when the ball starts falling from its peak height. The final velocity (v) is what we need to find, and the acceleration (a) is still -9.8 m/s². We can calculate the time taken for the ball to fall from the peak to the ground using the formula:

v = u + at

v = 0 + (-9.8)t

But we still need to find the time (t) taken for this part of the motion.

To find the total time of flight for the complete motion, we can use the fact that the time taken for the upward motion is equal to the time taken for the downward motion:

t_total = t_upwards + t_downwards

Once we have the total time of flight, we can calculate the final velocity (v) using the equation:

v = u + at

where u = 0, a = -9.8 m/s² (negative as it is in the downward direction), and t is the total time of flight.

To summarize, follow these steps to find the final velocity of the ball when it reaches the ground:

1. Calculate the time taken for the ball to reach its peak height using the equation v = u + at, where v = 0, u = 20 m/s, and a = -9.8 m/s².
2. Use the time calculated in step 1 to find the total time of flight, t_total = 2t_upwards.
3. Finally, calculate the final velocity of the ball using the equation v = u + at, where u = 0, a = -9.8 m/s², and t is the total time of flight calculated in step 2.