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Nonamiya [84]
3 years ago
6

Một đĩa tròn có bán kính 20cm đang đứng yên, được quanh nhanh dần đều sau 10s thì đạt vận tốc góc 180 vòng/phút. Hãy xác định: a

. Gia tốc góc của đĩa và số vòng đĩa quay được. b. Khi đang quay với 180 vòng/phút thì đĩa bị hãm phanh với lực không đổi sau 10s thì còn 90 vòng/phút. Tính gia tốc góc, số vòng và thời gian đĩa quay được kể từ lúc hãm phanh.
Physics
1 answer:
masya89 [10]3 years ago
7 0

this made my day happyf77d3

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A student lifts a 90 pound (lb) ball 4 feet (ft) in 5 seconds (s). How many joules of work has the student completed?
scZoUnD [109]

Wending your way through this question and the list of choices
is like running through a corn-maze on a moonless night with
your eyes closed.

Work = (force) x (distance)

Keeping with the units used In the question ...

       Work = (90 pounds) x (4 feet)  =  360 foot-pounds .

If you want the work expressed in joules, then you need to convert
pounds and feet to newtons and meters.

           (90 pounds) x (4.448 newtons/pound) =  400.32 Newtons

               (4 feet) x (1 meter / 3.28084 feet)  =  1.219 meters

Work = (force) x (distance)

          = (400.32 newtons) x (1.219 meters) = 488.1 joules .

7 0
3 years ago
3. What would the seasons be like if Earth's orbit had the eccentricity value of Mars?
densk [106]

Answer:

123456789

Explanation:

3 0
3 years ago
Read 2 more answers
How can cooler object can have more thermal energy than a warmer object?
Vladimir [108]
Temperature is only a measure of the average heat. It doesn't measure the quantity of heat. Even if a small cup of tea is really hot, it's so small. An iceberg is huge, and although cooler, will have much more heat, even if it's temperature is low
7 0
3 years ago
*100 points, please do all if not most of the questions listed, thank you*
e-lub [12.9K]

Answer:

1a.5km

2a. 31536000 seconds

2b.2800000 centimeters

2c.45,000,000 Milligrams

2d.0.0141667 m/s

2e.2.592 x 10^10 km/day

2f .8.23x10^-7m

2g.0.0000085 m3

Explanation:

1a.(25km/5)(1000m/1km)(1h/3600s) =(5km)( 1) (1) =5km

pls mark as brainliest

3 0
3 years ago
A projectile thrown from a point P moves in such a way that its distance from P is always increasing. Find the maximum angle abo
Anna71 [15]

Answer

70.52°

Explanation

The distance between projectile's position and it's starting point at any time is given by the relation

r² = x² + y²

where x = horizontal distance covered and y = vertical distance covered

According to projectile motion the horizontal displacement is given by

x = v(x)t = v cos(θ) t

Also the vertical component is given by

y = v(y) t - 0.5gt² = v sin(θ) t - 0.5gt²

Substituting the x and y values into the r-equation yields,

r² = (v cos(θ) t)² + (v sin(θ) t - 0.5gt²)²

r² = v²(cos²(θ))t² + v²(sin²(θ))t² – (vg sin(θ))t³+ 0.25 g²(t^4)

r² = v²t² (cos²(θ)+ sin²(θ)) – (vg sin(θ))t³ + 0.25 g²(t^4)

r² = v²t² – (vg sin(θ))t³ + 0.25 g²(t^4)

Differentiate r with respect to t

r(dr/dt) = 2v²t - 3vg sin(θ)t² + g²t³

At maximum angle the projectile could have been thrown above the horizontal, dr/dt = 0

2v²t - 3vg sin(θ)t² + g²t³ = 0

Divide through by t

2v² - 3vg sin(θ)t + g²t² = 0

g²t² - 3vg sin(θ)t + 2v² = 0

This can be solved using the general law for quadratic equations

(-b ± √(b² - 4ac))2a

a = g², b = -3vg sin(θ) c = 2v²

t = ((3vg sin(θ)) ± √(9v²g²sin²(θ) - 8g²v²))/2g²

This equation makes sense when the value under the square root is positive, that is, the square root exists.

9v²g²sin²(θ) - 8g²v² > 0

9sin²(θ) - 8 > 0

Meaning sin²(θ) = 8/9

Sin θ = (2√2)/3

θ = 70.52°

QED!!!

6 0
3 years ago
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