physics
posted by dipset
A 8kg ball is thrown up with an initial speed of 20m/s. Suppose there is a constant air resistence of 30N opposing the motion during its entire up and down path. How long will it take to get to the highest point in its path? how high is the highest point? How much work was done by the air resistence during the entire path up and down? What is the kinectic energy when it gets back to its original point?

drwls
I will be glad to critique your work.

dipset
I don't how to start it off

drwls
When the ball reaches its highest point H, potential energy will be
M g H = (1/2)MVo^2  f*H
where f is the friction force, 30N.
H = (1/2)MVo^2/(Mg + f)
Solve for H.
The time to get to that high point will be
T = H/Vo, since it will be decelerating at a constant rate.
The KE when it hits the ground will be M g H  f*H. This will equal
(1/2)MVo^2  2fH 
dipset
Thank you. one more question what would be the acceleration on the way up? on the way down?

Dr Russ
acceleration due to gravity

drwls
The acceleration is
g + (f/M) on the way up, and g  (f/M) on the way down. It is pointed down in both cases.
They are different because both g and friction point down on the way up, but are in opposite directions on the way down. For that reason, it arrives at the ground at a lower velocity than it took off.
Respond to this Question
Similar Questions

Physics
When baseball outfielders throw the ball, they usually allow it to take one bounce on the theory that the ball arrives sooner this way. Suppose that after the bounce the ball rebounds at the same angle theta as it had when released, … 
Physics
Ball is thrown horizontally off a cliff with an initial speed of 20m/s. a) how long does it take the ball to hit the ground 20m below. b)how long would it take to hit the ground if it was dropped from the cliff? 
physics
a 8 kg ball is thrown upward with an initial speed of 20 m/s. suppose there is a constant air resistance of 30N opposing the motion during it entire up and down path. what is the acceleration on the way up and on the way down? 
physics
A 5kg ball is thrown upward with an initial speed of 30m/s. Suppose there is a constant air resistance of 25N opposing the motion during its entire up and down path. How much work was done by air resistance during the entire path up … 
physics
A red ball is thrown down with an initial speed of 1.2 m/s from a height of 25.0 meters above the ground. Then, 0.6 seconds after the red ball is thrown, a blue ball is thrown upward with an initial speed of 22.9 m/s, from a height … 
Physics
A red ball is thrown down with an initial speed of 1.3 m/s from a height of 28.0 meters above the ground. Then, 0.6 seconds after the red ball is thrown, a blue ball is thrown upward with an initial speed of 24.7 m/s, from a height … 
Physics
A blue ball is thrown upward with an initial speed of 19.6 m/s, from a height of 0.5 meters above the ground. 2.4 seconds after the blue ball is thrown, a red ball is thrown down with an initial speed of 7.9 m/s from a height of 22.1 … 
Physics
A red ball is thrown down with an initial speed of 1.2 m/s from a height of 25 meters above the ground. Then, 0.6 seconds after the red ball is thrown, a blue ball is thrown upward with an initial speed of 22.9 m/s, from a height of … 
Physics
A red ball is thrown down with an initial speed of 1 m/s from a height of 27 meters above the ground. Then, 0.6 seconds after the red ball is thrown, a blue ball is thrown upward with an initial speed of 24.5 m/s, from a height of … 
physics
a 0.8kg ball is kicked with the speed 20m/s at an 50 to the horizontal.calculate the kinetic energy of the ball at maximum height. m=0.8kg v=20m/s h=?