A train starts from rest at station A and accelerates at 0.4 m/s^2 for 60 s. Afterwards it travels with a constant velocity for 25 min. It then decelerates at 0.8 m/s^2 until it is brought to rest at station B.
Determine the distance between the stations. ?s^Delta s = _______.

Respuesta :

The distance between the two stations is 37.08 km

[tex]\\[/tex]

Explanation:

Given:

[tex] a_1 \:=\:0.4\:m/s²[/tex]

[tex] t_1 \:=\:60\:s[/tex]

[tex] v_{i1} \:=\:0\:m/s[/tex]

[tex] a_2 \:=\:0\:m/s²[/tex]

[tex] t_2 \:=\:25\:min\:=\:1500\:s[/tex]

[tex] a_3 \:=\:-0.8\:m/s²[/tex]

[tex] v_{f3} \:=\:0\:m/s[/tex]

[tex]\\[/tex]

Required:

Distance from Station A to Station B

[tex]\\[/tex]

Equation:

[tex]a\:=\:\frac{v_f\:-\:v_i}{t}[/tex]

[tex]v_{ave}\:=\:\frac{v_i\:+\:v_f}{2}[/tex]

[tex]v\:=\:\frac{d}{t}[/tex]

[tex]\\[/tex]

Solution:

Distance when a = 0.4 m/s²

Solve for [tex]v_{f1}[/tex]

[tex]a\:=\:\frac{v_f\:-\:v_i}{t}[/tex]

[tex]0.4\:m/s²\:=\:\frac{v_f\:-\:0\:m/s}{60\:s}[/tex]

[tex]24\:m/s\:=\:v_f\:-\:0\:m/s[/tex]

[tex]v_f\:=\:24\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]v_{ave1}[/tex]

[tex]v_{ave}\:=\:\frac{v_i\:+\:v_f}{2}[/tex]

[tex]v_{ave}\:=\:\frac{0\:m/s\:+\:24\:m/s}{2}[/tex]

[tex]v_{ave}\:=\:12\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]d_1[/tex]

[tex]v\:=\:\frac{d}{t}[/tex]

[tex]12\:m/s\:=\:\frac{d}{60\:s}[/tex]

[tex]720\:m\:=\:d[/tex]

[tex]d_1\:=\:720\:m[/tex]

[tex]\\[/tex]

Distance when a = 0 m/s²

[tex]v_{f1}\:=\:v_{i2}[/tex]

[tex]v_{i2}\:=\:24\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]v_{f2}[/tex]

[tex]a\:=\:\frac{v_f\:-\:v_i}{t}[/tex]

[tex]0\:m/s²\:=\:\frac{v_f\:-\:24\:m/s}{1500\:s}[/tex]

[tex]0\:=\:v_f\:-\:24\:m/s[/tex]

[tex]v_f\:=\:24\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]v_{ave2}[/tex]

[tex]v_{ave}\:=\:\frac{v_i\:+\:v_f}{2}[/tex]

[tex]v_{ave}\:=\:\frac{24\:m/s\:+\:24\:m/s}{2}[/tex]

[tex]v_{ave}\:=\:24\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]d_2[/tex]

[tex]v\:=\:\frac{d}{t}[/tex]

[tex]24\:m/s\:=\:\frac{d}{1500\:s}[/tex]

[tex]36,000\:m\:=\:d[/tex]

[tex]d_2\:=\:36,000\:m[/tex]

[tex]\\[/tex]

Distance when a = -0.8 m/s²

[tex]v_{f2}\:=\:v_{i3}[/tex]

[tex]v_{i3}\:=\:24\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]v_{f3}[/tex]

[tex]a\:=\:\frac{v_f\:-\:v_i}{t}[/tex]

[tex]-0.8\:m/s²\:=\:\frac{0\:-\:24\:m/s}{t}[/tex]

[tex](t)(-0.8\:m/s²)\:=\:-24\:m/s[/tex]

[tex]t\:=\:\frac{-24\:m/s}{-0.8\:m/s²}[/tex]

[tex]t\:=\:30\:s[/tex]

[tex]\\[/tex]

Solve for [tex]v_{ave3}[/tex]

[tex]v_{ave}\:=\:\frac{v_i\:+\:v_f}{2}[/tex]

[tex]v_{ave}\:=\:\frac{24\:m/s\:+\:0\:m/s}{2}[/tex]

[tex]v_{ave}\:=\:12\:m/s[/tex]

[tex]\\[/tex]

Solve for [tex]d_3[/tex]

[tex]v\:=\:\frac{d}{t}[/tex]

[tex]12\:m/s\:=\:\frac{d}{30\:s}[/tex]

[tex]360\:m\:=\:d[/tex]

[tex]d_3\:=\:360\:m[/tex]

[tex]\\[/tex]

Total Distance from Station A to Station B

[tex]d\:= \:d_1\:+\:d_2\:+\:d_3[/tex]

[tex]d\:= \:720\:m\:+\:36,000\:m\:+\:360\:m[/tex]

[tex]d\:= \:37,080\:m[/tex]

[tex]d\:= \:37.08\:km[/tex]

[tex]\\[/tex]

Final Answer:

The distance between the two stations is 37.08 km

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