a) 7 buses
b) 6.8 m
Explanation:
a)
The motion of the motorcycle is a projectile motion, so it consists of 2 independent motions:
- A uniform motion along the horizontal direction
- A uniformly accelerated motion along the vertical direction
The initial components of the velocity of the motorcycle are:
![v_x = u cos(32^{\circ})=(40.0)(cos 32^{\circ})=33.9 m/s\\v_y = u sin(32^{\circ})=(40.0)(sin 32^{\circ})=21.2 m/s](https://tex.z-dn.net/?f=v_x%20%3D%20u%20cos%2832%5E%7B%5Ccirc%7D%29%3D%2840.0%29%28cos%2032%5E%7B%5Ccirc%7D%29%3D33.9%20m%2Fs%5C%5Cv_y%20%3D%20u%20sin%2832%5E%7B%5Ccirc%7D%29%3D%2840.0%29%28sin%2032%5E%7B%5Ccirc%7D%29%3D21.2%20m%2Fs)
The equation for the vertical motion of the motorcycle is
![y=h+u_y t - \frac{1}{2}gt^2](https://tex.z-dn.net/?f=y%3Dh%2Bu_y%20t%20-%20%5Cfrac%7B1%7D%7B2%7Dgt%5E2)
where
y is the altitude at time t
h is the initial height
is the acceleration due to gravity
The bus top is at the same height of the initial ramp, so we have
![y=h](https://tex.z-dn.net/?f=y%3Dh)
And therefore, we can solve the equation for t, to find the time of flight:
![0=u_y t - \frac{1}{2}gt^2\\t(u_y-\frac{1}{2}gt)=0\\t=\frac{2u_y}{g}=\frac{2(21.2)}{9.8}=4.33 s](https://tex.z-dn.net/?f=0%3Du_y%20t%20-%20%5Cfrac%7B1%7D%7B2%7Dgt%5E2%5C%5Ct%28u_y-%5Cfrac%7B1%7D%7B2%7Dgt%29%3D0%5C%5Ct%3D%5Cfrac%7B2u_y%7D%7Bg%7D%3D%5Cfrac%7B2%2821.2%29%7D%7B9.8%7D%3D4.33%20s)
Now we find what is the horizontal distance covered by the motorcycle in its jump, which is given by:
![d=v_x t = (33.9)(4.33)=146.8 m](https://tex.z-dn.net/?f=d%3Dv_x%20t%20%3D%20%2833.9%29%284.33%29%3D146.8%20m)
And since each bus has a length of L = 20.0 m, the number of buses that the motorcycle can clear with its jump is:
![n=\frac{d}{L}=\frac{146.8}{20}=7.34](https://tex.z-dn.net/?f=n%3D%5Cfrac%7Bd%7D%7BL%7D%3D%5Cfrac%7B146.8%7D%7B20%7D%3D7.34)
So, 7 buses.
b)
In the previous problem, we saw that the total range of the motion of the motorcycle is
![d=146.8 m](https://tex.z-dn.net/?f=d%3D146.8%20m)
And we said that this corresponds to 7 buses.
Each bus has a length of
L = 20 m
So, the total length of 7 buses is
![L' = 7L=7(20)=140 m](https://tex.z-dn.net/?f=L%27%20%3D%207L%3D7%2820%29%3D140%20m)
Therefore, the range of the motorcycle is greater than the length of the buses by:
![\Delta x = d-L'=146.8-140 = 6.8 m](https://tex.z-dn.net/?f=%5CDelta%20x%20%3D%20d-L%27%3D146.8-140%20%3D%206.8%20m)
which means he will miss the last bus by 6.8 meters.