A motorcycle daredevil plans to ride up a 2.0-m-high, 20° ramp, sail across a 10-m-wide pool filled with hungry crocodiles, and land at ground level on the other side. He has done this stunt many times and approaches it with confidence. Unfortunately, the motor-cycle engine dies just as he starts up the ramp. He is going 11 m/s at that instant, and the rolling friction of his rubber tires (coefficient 0.02) is not negligible. Does he survive, or does he become croco-dile food? Justify your answer by calculating the distance he travels through the air after leaving the end of the ramp

Respuesta :

Answer:

He becomes a croco-dile food

Explanation:

From the question we are told that

    The height is h = 2.0 m

      The angle is  [tex]\theta = 20^o[/tex]

     The distance is  [tex]w = 10m[/tex]

       The speed is  [tex]u = 11 m/s[/tex]

       The coefficient of static friction is  [tex]\mu = 0.02[/tex]

At equilibrium the forces acting on the motorcycle are mathematically represented as

        [tex]ma = mgsin \theta + F_f[/tex]

where  [tex]F_f[/tex] is the frictional force mathematically represented as

            [tex]F_f =\mu F_x =\mu mgcos \theta[/tex]

where [tex]F_x[/tex] is the horizontal component of the force

substituting into the equation

            [tex]ma = mgsin \theta + \mu mg cos \theta[/tex]

            [tex]ma =mg (sin \theta + \mu cos \theta )[/tex]

               making  a the subject of the formula

      [tex]a = g(sin \theta = \mu cos \theta )[/tex]

          substituting values

      [tex]a = 9.8 (sin(20) + (0.02 ) cos (20 ))[/tex]

        [tex]= 3.54 m/s^2[/tex]

Applying " SOHCAHTOA" rule we mathematically evaluate that length of the ramp as  

             [tex]sin \theta = \frac{h}{l}[/tex]

making [tex]l[/tex] the subject

          [tex]l = \frac{h}{sin \theta }[/tex]

substituting values

        [tex]l = \frac{2}{sin (20)}[/tex]

           [tex]l = 5.85m[/tex]

Apply Newton equation of motion we can mathematically evaluate the  final velocity at the end of the ramp  as

      [tex]v^2 =u^2 + 2 (-a)l[/tex]

  The negative a means it is moving against gravity

      substituting values

      [tex]v^2 = (11)^2 - 2(3.54) (5.85)[/tex]

           [tex]v= \sqrt{79.582}[/tex]

              [tex]= 8.92m/s[/tex]

The initial velocity at the beginning of the pool (end of ramp) is composed of two component which is

    Initial velocity along the x-axis which is mathematically evaluated as

          [tex]v_x = vcos 20^o[/tex]

       substituting values

         [tex]v_x = 8.92 * cos (20)[/tex]

              [tex]= 8.38 m/s[/tex]

Initial velocity along the y-axis which is mathematically evaluated as

             [tex]v_y = vsin\theta[/tex]

      substituting values

             [tex]v_y = 8.90 sin (20)[/tex]

                  [tex]= 3.05 m/s[/tex]

Now the motion through the pool in the vertical direction can mathematically modeled as

        [tex]y = y_o + u_yt + \frac{1}{2} a_y t^2[/tex]

where [tex]y_o[/tex] is the initial height,

         [tex]u_y[/tex] is the initial velocity in the y-axis

    [tex]a_y[/tex]  is the  initial  acceleration in the y axis  with a constant value of ([tex]g = 9.8 m/s^2[/tex])

at the y= 0 which is when the height above ground is zero

      Substituting values

              [tex]0 = 2 + (3.05)t - 0.5 (9.8)t^2[/tex]

The negative sign is because the acceleration is moving against the motion

                 [tex]-(4.9)t^2 + (2.79)t + 2m = 0[/tex]

   Solving using quadratic formula

              [tex]\frac{-b \pm \sqrt{b^2 -4ac} }{2a}[/tex]

substituting values

             [tex]\frac{-3.05 \pm \sqrt{(3.05)^2 - 4(-4.9) * 2} }{2 *( -4.9)}[/tex]

                [tex]t = \frac{-3.05 + 6.9}{-9.8} \ or t = \frac{-3.05 - 6.9}{-9.8}[/tex]

                [tex]t = -0.39s \ or \ t = 1.02s[/tex]

since in this case time cannot be negative

             [tex]t = 1.02s[/tex]

At this time the position the  motorcycle along the x-axis is mathematically evaluated as

              [tex]x = u_x t[/tex]

               x  [tex]=8.38 *1.02[/tex]

                   [tex]x =8.54m[/tex]

So from this value we can see that the motorcycle would not cross the pool as the position is less that the length of  the pool