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lord [1]
3 years ago
5

You throw a 20-N rock vertically into the air from ground level. You observe that when it is a height 14.8m above the ground, it

is traveling at a speed of 25.0 m/s upward.
A) Use the work-energy theorem to find its speed just as it left the ground. What is it?
B) Use the work-energy theorem to find its maximum height. What is it?
Physics
1 answer:
VladimirAG [237]3 years ago
4 0

Answer:

(A) The speed just as it left the ground is 30.25 m/s

(B) The maximum height of the rock is 46.69 m

Explanation:

Given;

weight of rock, w = mg  = 20 N

speed of the rock at 14.8 m, u = 25 m/s

(a) Apply work energy theorem to find its speed just as it left the ground

work = Δ kinetic energy

F x d = ¹/₂mv² - ¹/₂mu²

mg x d = ¹/₂m(v² - u²)

g x d = ¹/₂(v² - u²)

gd = ¹/₂(v² - u²)

2gd = v² - u²

v² = 2gd  + u²

v² = 2(9.8)(14.8) + (25)²

v² = 915.05

v = √915.05

v = 30.25 m/s

B) Use the work-energy theorem to find its maximum height

the initial velocity of the rock = 30.25 m/s

at maximum height, the final velocity = 0

- mg x H = ¹/₂mv² - ¹/₂mu²

- mg x H = ¹/₂m(0) - ¹/₂mu²

- mg x H = - ¹/₂mu²

2g x H = u²

H = u² / 2g

H = (30.25)² / 2(9.8)

H = 46.69 m

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A physicist makes a cup of instant coffee and notices that, as the coffee cools, its level drops 3.00 mm in the glass cup. Show
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Answer:

change in height  is 1.664 mm

Explanation:

Given data

drops = 3.00 mm

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decrease  =  350 cm^3

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the decrease in millimeters in level

solution

we  will calculate here change in volume so we can find how much level is decrease

change in volume = β v change in temp   ...............1

here change in volume = area× height

so = \pi /4 × d² h

so we can say change in volume =  \pi /4 × d² × change in height   .......2

so from equation 1 and 2  we calculate change in height

( β(w) -β(g) )× v× change in temp = \pi /4 × d² × change in height

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3 years ago
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