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soldier1979 [14.2K]
3 years ago
15

A string is wrapped several times around the rim of a small hoop with a radius of 8.00 cm and mass 0.180 kg. The free end of the

string is held in place and the hoop is released from rest.
After the hoop has descended 75.0 cm, calculate (a) the angular speed of the rotating hoop and (b) the speed of its center.
Physics
1 answer:
LekaFEV [45]3 years ago
8 0

Answer:

Vcm = 2.71m/s

Explanation:

From the problem description, the upper end is held fixed and not pulled upward so no work is done on the system of the hoop and string by holding this end of the string.

Mechanical energy is conserved because the string does not slip, although there is friction between the string and hoop.

So we can use the equation of conservation of mechanical energy.

K1 + U1 = K2 + U2

K1, K2 = initial and final kinetic energies of the system

U1, U2 = initial and final potential energies

Vcm = velocity of the center of mass of the system.

R = radius of the hoop

K1 = 0 system was initially at rest

U1 = mgh

K2 = 1/2MVcm² + 1/2×I×ω²

I = moment of inertia of the loop

I = MR²

ω = Vcm/R = Angukar frequency

K2 = 1/2×MVcm² + 1/2× MR² ×(Vcm/R)²

K2 = 1/2MVcm² + 1/2MVcm²

K2 = MVcm²

U2 = 0 chosen reference point as the system falls a distance of h

h = 75cm = 0.75m

Substituting the respective terms in the mechanical energy conservation equation above

0 + Mgh = MVcm² + 0

Mgh = MVcm²

gh = Vcm²

Vcm = √gh = √9.8×0.75 = 2.71m/s.

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The Burj Khalifa in Dubai is the world's tallest building. The structure is 828 m 828 m (2716.5 ft) and has more than 160 storie
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h = height of the hotel room from the ground floor = 237.4m

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Three people pull simultaneously on a stubborn donkey. Jack pulls eastward with a force of 80.5 N, Jill pulls with 81.7 N in the
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Answer:

F = 233.52 N,  θ' = 351.41º

Explanation:

In this exercise we must find the net force applied on the donkey.

For this we use Newton's second law, where we create a reference frame with the horizontal x axis

let's decompose the forces

Jack

        = 80.5 N

Jill

       cos 45 = F_{2x} / F₂2

       sin 45 = F_{2y} / F₂2

       F_{2x} = F₂ cos 45

       F_{2y} = F₂ sin 45

       F_{2x} = 81.7 cos 45 = 57.77 N

       F_{2y} = 81.7 sin 45 = 57.77 N

Jane

      cos (270 + 45) = F_{3x} / F₃3

      sin 315 = F_{3y} / F₃

      F_{3x} = 131 cos 315 = 92.63 N

      F_{3y} = 131 sin 315 = -92.63 N

the force can be found in each axis

X axis

         F_{x} = F_{1x} + F_{2x} + F_{3x}

         F_{x} = 80.5 +57.77 + 92.63

         F_{x} = 230.9 N

Axis y

         F_{y} = F_{1y} + F_{2y} + F_{3y}

         F_{y} = 0 + 57.77 -92.63

         F_{y} = -34.86 N

we can give the result in two ways

a) F = (230.9 i ^ - 34.86 j ^) N

b) in the form of module and angle

we use the Pythagorean theorem

         F = √(Fₓ² + F_{y}²

        F = √(230.9² + 34.86²)

        F = 233.52 N

let's use trigonometry for the angle

        tan θ = \frac{F_y}{F_x} }

        θ = tan⁻¹ (\frac{F_y}{F_x} })

        θ = tan⁻¹ (-34.86 / 230.9)

        θ = -8.59º

if we measure this angle from the positive side of the x-axis counterclockwise

          θ' = 360 -θ

          θ‘= 360- 8.59

          θ' = 351.41º

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3 years ago
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