Who can answer this Physics Challenge?

Question

A person standing on the edge of a cliff throws a ball straight up with speed 'u', allowing it to crash on to the rocks below. He later throws a ball with the same speed 'u' straight down. Which ball has the higher speed when it hits the rocks? (Neglect air resistance and assume acceleration due to gravity = -10 metres per second per second)
(Please show how you got the answer!! Best responce gets 10 Points!!)

Answer 1

Both balls would hit the rocks at the same speed.
Ball #1 would leave your hand travelling straight up at speed 'u'. It travels up, stops, and starts plummeting back to earth. When it reaches the height at which it left your hand, it is travelling at speed 'u' straight down. The speed that it hits the rocks at is u+(time x 10m/s/s).

Ball #2 would leave your hand travelling straight down at speed 'u'. The speed that it hits the rocks at is u+(time x 10m/s/s). It is the same speed.

Answer 2

CASE 1: THE BALL IS THROWN UP WITH A SPEED OF U.

We take the direction upward as positive. The initial position as origin.

The acceleration due to gravity acts downward. Hence it is a = -g.

The displacement is the distance between the origin and the final position of the ball.

Therefore S = - H.

We use the equation V V = U U + 2 a S.

The equation becomes V V = U U - 2 g (-H) = U U + 2 g H

CASE 1: THE BALL IS THROWN DOWN WITH A SPEED OF U.

As before, we take the upward direction as positive.

The initial speed is then negative as it goes down.

The initial position as origin.

The acceleration due to gravity acts downward. Hence it is a = -g.

The displacement is the distance between the origin and the final position of the ball.

Therefore S = - H.

We use the equation V V = U U + 2 a S.

The equation becomes V V =( -U) x (- U ) - 2 g (-H) = U U + 2 g H.

Thus in both the cases we get the same value for V.


ANOTHER EXPLANATION.

The ball (thrown up) returns to the cliff (from which it is thrown) with the same velocity but in the down ward direction. There after it falls down to the rock.

Thus there is no difference between the balls thrown up and thrown down as far as the final speed is concerned.

Answer 3

i dont get the 'U' part, but if i understand this right...
for every action there is an equal and opposite reaction so assuming u threw the ball up with x force, the ball would come down with X force until it was even with the point of release. since it wouls increase at a constant rate, iw would hit the ground at (f)x. the same would be true with the ball thrown down. but would the function [f] be the same? i am inclined to believe that the ball thrown down would be faster, but logically, i think that they would be the same.

Answer 4

ball thrown down final speed is v^2 = u^2+2gs
where s is height of the cliff so v = sqrt(u^2 + 2gs)
for ball thrown up the height gaines at the top is when v is equal to zero u^2-2gx = 0 (-ve as against gravity, x height above the cliff)
or x = u^2/2g
so now height is x+s inital velocity is 0 so final velocity is
v^2 = 2g(x+s) = 2g(u^2/2g +s)
or v^2 = u^2 + 2gs or v=sqrt(u^2 + 2gs)
so both final velocities are same.
if u have values of s and u^2 you can find final velocity.
hope this helps

Answer 5

I have heard of these gadgets, only I have seen ones that you strap on your arm as you run. Most likely you are not changing the aerodynamics of your car enough to cause a noticeable decrease in gas millage. It would be equivalent to sticking your hand out of the car or opening the window. It is a money saver because you are using the motion you are already creating and capturing more energy. You could also do this by plugging it into your car charge port. The only difference is that the wind turbine could be used other places to charge the phone, like your arm or just outside if the wind is brisk.

Answer 6

The velocity is equal since u=u, if you had given the mass of the ball is different then it could have been different. Hey wait without air resistance everything would be equal.
Remember the experiment of hammer and feather on Moon(Vaccum)

Answer 7

The ball thrown downward.

Vf = u - 20s ---> derived from the original Final velocity equation: Vf = Vi +2as, where 'Vf' is final velocity, 'Vi' is intial velocity, 'a' is acceleration due to gravity and 's' is your displacement from the ground.

As 's' gets larger, your final velocity will in turn get smaller.

Answer 8

They should both hit the ground with equal force!

Answer 9

the anwer is:
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i wont wet 10 points

Answer 10

Yes, is the answer!