In a downhill ski race, your final velocity is not affected very much by getting a running start, because the initial kinetic energy is small compared with the gain in gravitational potential energy on even small hills. However, you will finish the race much faster (which is more important!). To demonstrate this, find the final speed and the time taken for a skier who skies 75 m along a slope that is 29°, measured from horizontal, in the following situations (you may neglect friction). 25% Part (a) Find the final speed (in ms) of the skier starting from rest. Grade Summa Pes 0% 100% Potential cosO cotan asin acos0 atan0 acotan sinh cosh0nh0cotanh0 SubmissionS Attempts remaining: 4 % per attempt) detailed view Degrees O Radians Submit Hint I give up! Hints: 096 deduction per hint. Hints remaining: 3 Feedback: 1% deduction per feedback. 25% Part (b) How long (in s) does it take for the skier to reach the bottom of this hill starting from rest? là 25% Part (c) Find the final speed (in ms) ofthe skier starting with a speed of 2.50 m/s. 25% Part (d) How long (in s) does it take for the skier to reach the bottom of this hill with a starting speed of 2.50 ms?

Respuesta :

Answer:

(a) [tex]v_f= 26.7095 m/s[/tex]

(b) 5.615979

(c) [tex]v_f= 26.82624 m/s[/tex]

(d) t=5.114872571 seconds

Explanation:

(a)

Acceleration, a along the slope is given by

[tex]a=gsin\theta[/tex] where g is acceleration due to gravity and [tex]\theta[/tex] is the angle of inclination

Also, the velocity after moving a distance s is given by

[tex]v_f^{2}=v_i^{2}+2as[/tex] where [tex]v_f[/tex]  and [tex]v_i[/tex] are final and initial velocities, s is distance covered

Substituting [tex]a=gsin\theta[/tex] into the above we obtain

[tex]v_f^{2}=v_i^{2}+2sgsin\theta[/tex]

Making [tex]v_f[/tex] the subject we obtain

[tex]v_f=\sqrt{v_i^{2}+22sgsin\theta}[/tex] and substituting [tex]9.81 m/s^{2}[/tex] for g, [tex] 29^{0}[/tex] for [tex]\theta[/tex] and 75 m for s while initial velocity is zero

[tex]v_f=\sqrt {2sgsin\theta}=\sqrt {2*75*9.81sin29}[/tex]

[tex]v_f= 26.7095 m/s[/tex]

(b)  

Time to reach the bottom is given by

[tex]v_f=v_i+at=v_i+gtsin\theta[/tex] and making t the subject of the formula

[tex]t=\frac {v_f-v_i}{gsin\theta}[/tex] but since initial velocity is zero hence

[tex]t=\frac {v_f}{gsin\theta}=\frac {26.696}{9.81sin29^{o}}= 5.615979 seconds[/tex]

(c)

When the initial velocity is 2.5 m/s then

[tex]v_f=\sqrt {V_i^{2}+2sgsin\theta}[/tex]

[tex]v_f=\sqrt {2.5^{2}+(2*9.81*75sin29^{o}}[/tex]

[tex]v_f= 26.82624 m/s[/tex]

(d)

Time required to reach the bottom is given by

[tex]t=\frac {v_f-v_i}{a}=\frac {v_f-V_i}{gsin\theta}[/tex] and substituting the above figures we get

[tex]t=\frac {26.82624-2.5}{9.81sin29^{o}}[/tex]

t=5.114872571 seconds