A worker kicks a flat rock lying on a roof. The rock slides up the incline 10.0 m to the apex of the roof, and flies off the roof as a projectile. What maximum height (in m) does the rock attain? Assume air resistance is negligible, vi = 15.0 m/s, μk = 0.425, and that the roof makes an angle of θ = 42.0° with the horizontal. (Assume the worker is standing at y = 0 when the rock is kicked.)

Respuesta :

Answer:

h = 7.42 m

Explanation:

deceleration of the rock

[tex]a = g sin \theta + \mu_kgcos \theta[/tex]

[tex]a = 9.8 sin 42^0+0.425\times 9.8 \times cos 42^0[/tex]

a = 9.65 m/s²

using formula

v² = u² + 2 a s

v² = 15² - 2×9.65 × 10

v = 5.66 m/s

the height attained is

h₁ =  10 sin θ

   = 10 sin 42

   = 6.69 m

now with vertical velocity it will reach to the height h₂

v y = v sin θ

     = 5.66 sin 42

     = 3.79 m/s

height is

v² = u² + 2 a s

0 = 3.79² - 2 × 9.8 ×h₂

h₂ = 0.73 m

the maximum height is

h = h₁ + h₂

  = 6.69 + 0.73

h = 7.42 m

The maximum height that the rock attains is : 7.42 m

Given data :

Vi = 15.0 m/s

uk = 0.425

angle made by roof ( θ ) = 42.0°

Calculating the maximum height reached by the rock

First step : calculate the deceleration of the rock

a = g*sinθ + uk * g * cosθ

  = 9.8 * sin 42° + 0.425 * 9.8 * cos 42°

  = 9.65 m/s²

Applying motion formula

v² = u² + 2as

    = 15² - 2 * 9.65 * 10

 v  = 5.66 m/s

Initial height attained ( h₁ ) =  10 sin θ

                                           =  10 * sin 45°

                                           =  6.69 m

considering vertical height

V (y) = v sin θ

       = 5.66 sin 42

       = 3.79 m/s

Next step : Calculate  height ( h₂ )

v² = u² + 2 a s

0 = 3.79² - 2 * 9.8 * h₂

therefore :  h₂ = 0.73 m

The maximum height attained by the rock ( H ) = h₁ + h₂

                                                                              = 6.69 + 0.73 = 7.42 m

Hence we can conclude that The maximum height that the rock attains is : 7.42 m

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