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NemiM [27]
3 years ago
15

A factory worker pushes a 30.0-kg crate a distance of 4.5 m along a level floor at constant velocity by pushing horizontally on

it. the coefficient of kinetic friction between the crate and the floor is 0.25. (a) what magnitude of force must the worker apply
Physics
1 answer:
Olin [163]3 years ago
5 0
The crate moves at constant velocity, this means that its acceleration is zero, so the net force acting on the crate is zero (Newton's second law). 

There are only two forces acting on the crate: the force F applied by the worker and the frictional force, acting in the opposite direction: \mu m g, where \mu=0.25 is the coefficient of friction and m=30.0 kg is the mass of the crate. Since the net force should be equal to zero, the two forces must have same magnitude, so we have:
F=\mu m g=(0.25)(30.0 kg)(9.81 m/s^2)=73.8 N
And so, this is the force that the worker must apply to the crate.
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Calculate the pH of hydronium ions in a 0.000 01 M solution of the strong acid HI.
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<h3>Answer:</h3>

pH = 5

<h3>Explanation:</h3>

<u>We are given;</u>

  • Concentration of a solution HI as 0.00001 M

We are required to calculate the pH of Hydronium ions.

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HI + H₂O → H₃O⁺(aq) + I⁻(aq)

  • Therefore;
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you will For this problem, you will need to look up physical parameters for objects in space want to keep about 4 significant fi
Tanzania [10]

Answer:

a)  r₁ = 3.836 10⁷ m,  b)   F = - 3,390 10⁸ N , c)  R = 120.3 m

Explanation:

a) This is a problem of equilibrium where the force is gravitational, we call F1 the force of the Moon and F2 the force from the earth.

       F₁ -F₂ = 0

       F₁ = F₂

       G m M_{m} / r₁² = G m M_{e} / r₂²

Let's look for the measured distance from a Coordinate System located on the Moon,

         r₂ = D - r₁

Where D is the average distance from Terra to the Moon 3.84 10⁸ m

        M_{m} / r₁² = M_{e} / (D - r₁)²

       (D² - 2 D r₁ + r₁²) = M_{e} /M_{m} r₁²

       (1 - M_{e} / M_{m})r₁² - 2D r₁ + D² = 0

Let's replace and solve the second degree equation

       (1 - 5.98 10²⁴ / 7.36 10²²) r₁² - 2 3.84 10⁸ r₁ + (3.84 10⁸)² = 0

       -80.25 r₁² - 7.68 10⁸ r₁ + 14.75 10¹⁶ = 0

        r₁² + 9.57 10⁶ r₁ - 1.838 10¹⁵ = 0

        r₁ = [-9.57 10⁶ ±√ (91.58 10¹² + 7.352 10¹⁵)] / 2

        r₁ = [-9.57 10⁶ + - 86.28 10⁶] / 2

The results are:

       r₁’= 38.355 10 6 m

       r₁ ’’ = -47.915 10 6 m

We take the positive result that a distance between the moon and the Earth, the equalization point is    r₁ = 3.836 10⁷ m

b) The force at point R = 2 r₁

        R = 2 3.8355 10⁷ = 7.671 10⁷ m

        F = F₁ - F₂

        F = G m  M_{m} / R² - G m  M_{e} / (D- R)²

        F = G m ( M_{m} / R² -  M_{e} / (D-R)²)

   F = m 6.67 10⁻¹¹ (7.36 10²² / (7.671 10⁷)² - 5.98 10²⁴ / (3.84 10⁸ - 0.7671 10⁸)²

        F = m 6.67 10⁻¹¹ (0.125076 10⁸ - 0.63329 10⁸)

        F = m (-3.3897 10⁸) N

The mass m of the rocket must be known, suppose it is worth 1 kg (m = 1 kg)

        F = - 3,390 10⁸ N

c) let's use gravitational force from the moon

        F = G m  M_{m} / R²

        R =√ G m  M_{m} / F

        R = √ (6.67 10⁻¹¹ 1 7.36 10²² / 3.3897 10⁸)

        R = √ (1.4482 10⁴)

        R = 1.2034 10² m

        R = 120.3 m

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