A stationary car is stopped at a traffic light. When the light turns green at t = 0, a truck with a constant speed of 25m/s passes the car. The car uniformly accelerates to its top speed (30m/s) in 10 s then moves at a constant speed. How long will it take for the car to catch up with the truck?​

Respuesta :

It will take the car 16.67 sec to catch up with the truck.

Given the data in the question.

Since the car was stationary, then;

Initial velocity of the car; [tex]u_c = 0m/s[/tex].

Final velocity of the car; [tex]v_c = 30m/s[/tex].

Time taken for the car to reach given speed; [tex]t = 10s[/tex].

At [tex]t = 0[/tex], speed of truck; [tex]V_{truck} = 25m/s[/tex]

First, we find the acceleration of the car, using the first equation of motion;

[tex]v = u + at[/tex]

We make "a" the subject of the formula,

[tex]a = \frac{v-u}{t}[/tex]

We substitute in our values and solve for "a"

[tex]a = \frac{30m/s - 0m/s}{10s}[/tex]

[tex]a = 3m/s^2[/tex]

Now, to determine how long will it take for the car to catch up with the truck.

Distance travelled by truck should be equal to distance travelled by car, so;

[tex]S_{truck[/tex] = [tex]S_{car[/tex]

We know that, speed; s = distance / time

So, distance of truck [tex]S_{truck[/tex] = speed of truck × time [tex]= V_{truck} * t[/tex]

Also, from the second equation of motion; distance "s" is;

[tex]s = ut + \frac{1}{2}at^2[/tex]

So distance of the car [tex]S_{car} = ut + \frac{1}{2}at^2[/tex]

We equate

[tex]S_{truck[/tex] = [tex]S_{car[/tex]

[tex]V_{truck} * t[/tex] [tex]= ut + \frac{1}{2}at^2[/tex]

we make "t" the subject of formula

we know that initial velocity of the car; u = 0

so, we divide both sides by "t"

[tex]V_{truck} = \frac{1}{2}at[/tex]

[tex]t = \frac{2V_{truck}}{a}[/tex]

We substitute in our values

[tex]t = \frac{2 * 25m/s}{3m/s^2}[/tex]

[tex]t = 16.67s[/tex]

Therefore, It will take the car 16.67 sec to catch up with the truck.

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