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Romashka-Z-Leto [24]
3 years ago
10

A 60-kg runner raises his center of mass approximately 0.5 m with each step. Although his leg muscles act as a spring, recapturi

ng the energy each time his feet touch down, there’s an average 10% loss with each compression. What must the runner’s additional power output be to account for just this loss, if he averages 0.8 s per stride?
Physics
1 answer:
Darina [25.2K]3 years ago
5 0

Answer: P = 36.75W

The additional power needed to account for the loss is 36.75W.

Explanation:

Given;

Mass of the runner m= 60 kg

Height of the centre of gravity h= 0.5m

Acceleration due to gravity g= 9.8m/s

The potential energy of the body for each step is;

P.E = mgh

P.E = 60 × 9.8 × 0.5

PE = 294J

Since the average loss per compression on the leg is 10%.

Energy loss = 10% (P.E)

E = 10% of 294J

E = 29.4J

To calculate the runner's additional power

given that time per stride is = 0.8s

Power P = Energy/time

P = E/t

P = 29.4J/0.8s

P = 36.75W

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Three people pull simultaneously on a stubborn donkey. Jack pulls directly ahead of the donkey with a force of 63.9 N63.9 N , Ji
Greeley [361]

Answer:

a) F = (137.4 i ^ + 185 j ^) N

b)    F = 230.2 N  ,  θ = 53.5º

Explanation:

In this exercise we ask to find the net force, for which we will define a coordinate system fix the donkey and use trigonometry to decompose the forces

Jack       F₁ₓ = 63.9 N

Jill          F₂ = 79.1 N with direction 45º to the left

              cos (180 -45) = F₂ₓ / F₂

              sin 135 = F_{2y} / F₂

              F₂ₓ = F₂ cos 135

              F_{2y} = F₂ sin 135

              F₂ₓ = 79.1 cos 135 = -55.9 N

              F_{2y} = 79.1 sin 135 = 55.9 N

Jane      F₃ = 183 N direction 45th to the right

             cos 45 = F₃ₓ / F3

             sin 45 = F_{3y} / F3

             F₃ₓ = F₃ cos 45 = 183 cos 45

             F_{₃y} = F₃ sin 45 = 183 sin 45

             F₃ₓ = 129.4 N

             F_{3y} = 129.4 N

we add each component of the force

       Fₓ = F₁ₓ + F₂ₓ + F₃ₓ

       Fₓ = 63.9 + (-55.9) + 129.4

       Fₓ = 137.4 N

       F_{y} = F_{2y} + F_{3y}

       F_{2y} = 55.9 + 129.4

       F_{2y} = 185.3 N

we can give the result of the forms

 

a) F = (137.4 i ^ + 185 j ^) N

b) in the form of module and angle

         F = RA (Fₓ² + F_{y}²)

         F = Ra (137² + 185²)

         F = 230.2 N

         tan θ = F_{y} / Fₓ

         θ = tan⁻¹ F_{y} / Fₓ

        θ = tan⁻¹ (185/137)

        θ = 53.5º

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A point charge q1 = -8.9 μC is located at the center of a thick conducting shell of inner radius a = 2.8 cm and outer radius b =
musickatia [10]

Answer:

1) Ex(P) = -8.34602 N/C

2) E_y(P) = -5.23850174216 N/C

3) Question (3) is a similar question to (1)

4) E_y(P) = -5.23850174216 N/C

5) \sigma _b ≈ 1.041466 C/m²

6) σₐ ≈ 2.2330413 C/m²

Explanation:

The given parameter of the point charge located at the center of a conducting shell

The charge of the point charge, q₁ = -8.9 μC

The inner radius of the shell, a = 2.8 cm

The outer radius of the shell, b = 4.1 cm

The charge of the conducting shell, q₂ = 2.2 μC

Therefore, we have;

1) The point P(8.5, 0)

V = k \cdot \dfrac{q_1 + q_2 }{r^2}

By plugging in the values, we have;

For

R₁ < R₂ < r, for the electric field at the point, 'P', we have;

E_x(P) = 9 \times 10^9 \times \dfrac{-8.9 \ \times 10^{-6} + 2.2 \ \times 10 ^{-6} }{(0.085 \ )^2} = -8.34602

Ex(P) = -8.34602 N/C

2) For the point given with coordinates (8.5, 0), the distance of the y-component of point from the center = 0

The y-component of the electric field = 0 N/C

4) For r = 1.4 cm, along the y-axis we have;

R₁ < r < R₂

Therefore, we have;

E = k \cdot \left( \dfrac{q_1 }{r} + \dfrac{q_2}{R_2}\right)

Substituting the values, we get;

E_y(P) = 9 \times 10^9 \times \left( \dfrac{-8.9 \times 10^{-6}}{0.014} + \dfrac{2.2 \times 10^{-6}}{0.041}\right) = -523850174216

E_y(P) = -5.23850174216 N/C

5) The charge density, \sigma _b, is given as follows;

\sigma_b = \dfrac{Q}{A}  = \dfrac{2.2 \times 10^{-6} }{4\times \pi  \times 0.041^2 } \approx 1.041466 \ C/m^2

6) Similarly, we have;

\sigma_a = \dfrac{Q}{A_a}  = \dfrac{2.2 \times 10^{-6} }{4\times \pi  \times 0.028^2 } \approx 2.2330413 \ C/m^2

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