A ball is thrown up with a velocity of 20 m/s. How long will it be before the ball returns to the ground? Assume gravitational acceleration = 10 m/s2. You can ignore air friction.

Question

anonymous · Answer

What's the weight of the ball?

anonymous · Answer

You have divide the flight into two parts:

First part : The ball is thrown vertically upwards until it has reached its maximum height.

Second part: The ball is falling down until it reaches the ground.

anonymous · Answer

Lets consider the first part:

Write the data and use it find the time when it reaches the maximum height:

initial velocity= 20m/s  

acceleration due to gravity= -10m/s2 because it is travelling away from gravity and acceleration is a vector quantity.

final velocity= 0m/s because it stops in the air when maximum height is reached.

time= ts

anonymous · Answer

From the equations of motion use the suitable equation to find time which is:

v=u+at     v-u=at    v-u/a=t

0-20/-10=t     t=2 seconds

anonymous · Answer

The ball took 2 seconds to reach the maximum height and will take the same time to return to the ground so:

2+2= 4 seconds

anonymous · Answer

The ball is in the air for 4 seconds.

anonymous · Answer

formula is 2u/g
therefore-2*20/10=4sec.

anonymous · Answer

Unless you know the weight of the ball and the speed at which it left the hand. The speed of the ball 
is not a constant if gravity is involved. Air friction would play a part on size, but the weight still is a factor. If the speed  is 20 m/s at start then weight has to be a factor. Question isn't broken down enough.