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emmainna [20.7K]
3 years ago
15

A child drops a ball from a window. The ball strikes the ground in 3.0 seconds. What is the velocity of the ball the instant bef

ore it it hits the ground
Physics
1 answer:
inessss [21]3 years ago
5 0

Answer:

29.396988 m/s

Explanation:

Really, it depends on where the child is when he drops the ball - e.g., which planet he is on, and his distance from the center of that planet.

I'll assume that the child is on Earth at sea level at the equator, so that his distance from the geocenter is 6378000 meters.

The acceleration, g, is found from

g = GM/r²

G = 6.6743e-11 m³ kg⁻¹ sec⁻²

M = 5.9724e+24 kg

r = 6.378e+6 m

g = 9.799086 m sec⁻²

An approximate answer is found from an equation from constant acceleration kinematics:

v = gt

t = 3.0 sec

v = 29.397259 m/s

Now, the above method is an approximation that makes the technically incorrect assumption that the acceleration of gravity is a constant throughout the entire fall. You get away with it because the drop is very short. In another situation, it might not be. So it would be nice to develop a more accurate method that does not assume constant gravitational acceleration. For that, we begin with the Vis Viva equation:

v = √[GM(2/r − 1/a)]

Here,

a = the semimajor axis of a plunge orbit, which is equal to half of the apoapsis distance of 6378000+h, where

h = the altitude from which the ball is dropped

We can (using some math) develop the following equation:

t − t₀ = √[d/(2GM)] { √(rd−r²) + d arctan √(d/r−1) }

t − t₀ = 3 sec

r = 6378000 meters

d = r + h

Using an iterative method (e.g. Newton's or Danby's), we can determine that the altitude,

h = 44.0954 meters

So,

d = 6378044.09538 meters

a = d/2 = 3189022.04769 meters

Now we can calculate that

v = 29.396988 m/s

This is the more nearly correct answer because it takes into account the variability of the gravitational acceleration during the fall.

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Explanation:

From the information given;

Using the work-energy theorem

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<u>169 Kcalories</u> are provided by a portion of food that has 25 grams of carbs, 6 grams of protein, and 5 grams of fat.

Kcalories mean kilo-calories. Basically, kilo-calorie or kcal refers to 1,000 calories. To get the Kcalories of food, you have to add the kcal of carbohydrates, protein, and fat.

Get the product by multiplying the number of grams of carbohydrate, protein, and fat by 4,4, and 9, respectively. So if you want to get the energy or Kcal available from a meal, you must then combine the outcomes.

Simply put it, take note of the following conversions:

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  • 1 gram of protein is also 4kcal
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So here's how to compute the Kcalories of food that contains 25g carbs, 6g protein, and 5g fat.

1.    25g x 4kcal/g = 100kcal

2.    6g x 4kcal/g = 24kcal

3.    5g x 9kcal/g = 45kcal

4.    100kcal + 24kcal + 45kcal = 169kcal!


Therefore, the food contains 169 kilo-calories!

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Answer:False

Explanation:

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When we pull the door by a force it causes zero displacements of the door. So we can say that work done on it is zero.

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