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Find the velocity function.

Computer Science

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Answers

2 parts
a

2 s and 4.5 s\text{2 s and 4.5 s}

b

5 m\text{5 m}

Step-by-step solution

5 steps

Part a· 2 steps

  1. Find the velocity function.

    The acceleration is given by a=(4t−13) ms−2a = (4t - 13) \text{ ms}^{-2}.
    Velocity vv is the integral of acceleration with respect to time tt.

    v=∫a dt=∫(4t−13) dtv = \int a \, dt = \int (4t - 13) \, dt v=2t2−13t+Cv = 2t^2 - 13t + C

    We are given that the initial velocity is 18 ms−118 \text{ ms}^{-1}, which means v=18v = 18 when t=0t = 0.
    Substitute these values to find CC:

    18=2(0)2−13(0)+C18 = 2(0)^2 - 13(0) + C C=18C = 18

    So, the velocity function is:

    v=2t2−13t+18v = 2t^2 - 13t + 18
  2. Determine tt when the particle is momentarily at rest.

    The particle is momentarily at rest when its velocity v=0v = 0.

    2t2−13t+18=02t^2 - 13t + 18 = 0

    We can solve this quadratic equation by factorization. We need two numbers that multiply to 2×18=362 \times 18 = 36 and add up to −13-13. These numbers are −4-4 and −9-9.

    2t2−4t−9t+18=02t^2 - 4t - 9t + 18 = 0 2t(t−2)−9(t−2)=02t(t - 2) - 9(t - 2) = 0 (2t−9)(t−2)=0(2t - 9)(t - 2) = 0

    This gives two possible values for tt:

    2t−9=0  ⟹  2t=9  ⟹  t=92=4.5 s2t - 9 = 0 \implies 2t = 9 \implies t = \frac{9}{2} = 4.5 \text{ s} t−2=0  ⟹  t=2 st - 2 = 0 \implies t = 2 \text{ s}

    The values of tt when the particle is momentarily at rest are 2 s and 4.5 s\boxed{\text{2 s and 4.5 s}}.

Part b

5 m\text{5 m}

  1. Find the position function.

    Position ss is the integral of velocity with respect to time tt.

    s=∫v dt=∫(2t2−13t+18) dts = \int v \, dt = \int (2t^2 - 13t + 18) \, dt s=23t3−132t2+18t+Ds = \frac{2}{3}t^3 - \frac{13}{2}t^2 + 18t + D

    For calculating distance covered, the constant DD will cancel out, so we can set D=0D=0.

    s(t)=23t3−132t2+18ts(t) = \frac{2}{3}t^3 - \frac{13}{2}t^2 + 18t
  2. Check for changes in direction within the interval $[1, 3]$ s.

    From part (a), we know the particle is momentarily at rest at t=2t = 2 s and t=4.5t = 4.5 s.
    The value t=2t = 2 s lies within the interval [1,3][1, 3] s. This means the particle changes direction at t=2t=2 s. Therefore, we must calculate the distance covered in two separate intervals: [1,2][1, 2] s and [2,3][2, 3] s, and sum their absolute displacements.

  3. Calculate the distance covered.

    Displacement from t=1t=1 to t=2t=2:

    s(2)=23(2)3−132(2)2+18(2)=163−26+36=163+10=16+303=463 ms(2) = \frac{2}{3}(2)^3 - \frac{13}{2}(2)^2 + 18(2) = \frac{16}{3} - 26 + 36 = \frac{16}{3} + 10 = \frac{16 + 30}{3} = \frac{46}{3} \text{ m} s(1)=23(1)3−132(1)2+18(1)=23−132+18=4−39+1086=736 ms(1) = \frac{2}{3}(1)^3 - \frac{13}{2}(1)^2 + 18(1) = \frac{2}{3} - \frac{13}{2} + 18 = \frac{4 - 39 + 108}{6} = \frac{73}{6} \text{ m}

    Displacement Δs1=s(2)−s(1)=463−736=92−736=196 m\Delta s_1 = s(2) - s(1) = \frac{46}{3} - \frac{73}{6} = \frac{92 - 73}{6} = \frac{19}{6} \text{ m}.

    Displacement from t=2t=2 to t=3t=3:

    s(3)=23(3)3−132(3)2+18(3)=18−1172+54=72−1172=144−1172=272 ms(3) = \frac{2}{3}(3)^3 - \frac{13}{2}(3)^2 + 18(3) = 18 - \frac{117}{2} + 54 = 72 - \frac{117}{2} = \frac{144 - 117}{2} = \frac{27}{2} \text{ m}

    Displacement Δs2=s(3)−s(2)=272−463=81−926=−116 m\Delta s_2 = s(3) - s(2) = \frac{27}{2} - \frac{46}{3} = \frac{81 - 92}{6} = -\frac{11}{6} \text{ m}.

    Total distance covered is the sum of the absolute values of the displacements:

    Total distance=∣Δs1∣+∣Δs2∣=∣196∣+∣−116∣\text{Total distance} = |\Delta s_1| + |\Delta s_2| = \left|\frac{19}{6}\right| + \left|-\frac{11}{6}\right| Total distance=196+116=306=5 m\text{Total distance} = \frac{19}{6} + \frac{11}{6} = \frac{30}{6} = 5 \text{ m}

    The distance covered by the particle between t=1t = 1 second and t=3t = 3 seconds is 5 m\boxed{\text{5 m}}.

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