Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
2 balls one thrown upwards and one dropped?
Ball A is dropped from the top of a building at the same instant that ball B is thrown vertically upward from the ground. When the balls collide they are moving in opposite directions, and the speed of A is twice the speed of B. At what fraction of the height of the building does the collision occur?
I know its 1/3 the height of the building but.....i cant seem to get there mathematically any one know how to?
p.s. ignore air resistance
4 Answers
- 1 decade agoFavorite Answer
First off...it's not actually 1/3 the height of the building that they meet at, it's at 2/3s of the height of the building (counting up from the ground that is).
If we start by defining the final velocity of ball B as our unit of velocity, then the final velocity of ball B is 1, and the final velocity of ball A is -2 (negative because it is going downwards). We know the initial velocity of ball A is 0, and because it is undergoing constant acceleration, its average velocity over the time of the experiment will be (initial + final) / 2, or -1.
Considering ball B, and knowing that all objects undergo the same acceleration due to gravity when air friction is ignored, we can conclude that its velocity has also decreased by two from its initial velocity, just as the velocity of ball A dropped from 0 to -2, so the initial velocity of ball B must have been 3 in order for it to still have a speed of 1 after the time interval of our experiment. So the average velocity of ball B over the experiment is (3 + 1) / 2 = 2.
Since we know the average velocity of ball A was -1, we can conclude it dropped a distance d = (average velocity) * time, or -1t (while units were left off in this example, it is always necessary to multiply velocity by time to get distance, e.g. 1 mile/hour * 1 hour = 1 mile). Over the same interval, Ball two rose the distance 2t. Since the height of the building = the distance ball B rose - the distance ball A fell, the building must be 3t in height, meaning that ball B rose 2/3s of the building height, and ball A fell 1/3 of the building's height.
- 1 decade ago
Let t be the time they need to meet. then the dropped ball has the speed
vA = g * t
while the rising ball has the speed
vB = 1/2 vA = 1/2 gt
Ball A fell
f = 1/2 g t^2
Ball B rose
r = 1/4 gt^2
the heigth is
h = r + f = 3/4 gt^2 = 3 * r
So
h = 3 * r ---> r = 1/3 * h
- 5 years ago
I am fixing map's solution above me.
Let t = t_o be the time they need to meet. Then the dropped ball has the speed
vA = g * t_o
while the rising ball has speed
vB = u - g*t_o
We are given vB = 1/2 * v_A
substituting g * t_o for vA
we have vB = 1/2 * g*t_0
So far we have
vB = 1/2 * g*t_o
vB = u - g*t_o
By equality
1/2 * g*t_0 = u - g*t_o
solving for u
u = 3/2*g*t_0
Ball A fell
f = 1/2 g t_o^2
Ball B rose
r = u*t_0 - 1/2*gt_o^2
substitute u = 3/2*g*t_o
Ball B rose
r = (3/2*g*t_o) * t_o - 1/2*gt_o^2
r = g*t_o^2
the heigth (sic) is
h = r+f = g*t_o^2 + 1/2*g*t_o^2 = 3/2 gt_o^2 = 3/2 * r
So
h = 3/2 * r ---> r = 2/3 * h
- mcneilLv 45 years ago
bypass on a internet site that assist you to understand methods many energy you're able to desire to stay on the load you're actually, there is an determination the place it says phisical activity it may be in mattress or scientific institution, then subtract 4 hundred energy to drop some weight. yet another element is make a smoothie of juice from 4 oranges, juice from a million grapefruit, a green apple sliced, 2 celery sticks, and a handful of decrease nopales( a mexican merchandise this is like cactus, be sure you're taking of the spines) you combination it at the same time and additionally you're able to pick a glass of water further too, then you definately drink all of it, you're able to desire to upload a tablespoon of powdered flax seeds for extra starvation administration. in case you get hungry later interior the day take slender speedy or a salad with mild dressing. in 5 days i've got lost a great type of inches and 10lbs. and that i did not even exercising in basic terms each and daily strikes, and if anybody says that's undesirable, that's not, people say that because of the fact once you drop some weight speedy after which you're able to desire to truly bypass on your previous behavior, yet its not undesirable. do not throw up i understand a female that died because of the fact of it.