April sits at rest on a skateboard. She has a mass of 65 kg. Her friend throws
her a suitcase (m= 15 kg) at a speed of 3 m/s. If she catches it, how fast will
she, the skateboard, and the suitcase move?


  1. Answer:

    Velocity = 0.5625m/s



    Represent mass of April with M and mass of the suitcase with m; such that

    M = 65kg

    m = 15kg

    Represent initial velocity of April with U and initial velocity of the suitcase with u; such that

    U = 0m/s (because she’s resting on the skateboard, initially)

    u = 3m/s

    After she catches the suitcase, she, the skateboard and the suitcase moves at the same velocity.

    Represent this velocity with v

    The above given information can be representing using law of conservation of momentum.

    MU + mu = (M + m)v

    Substitute the values of M,U, m and u.

    This gives

    65 * 0 + 15 * 3 = (65 + 15)v

    0 + 45 = (80)v

    45 = 80v

    Divide both sides by 80

    \frac{45}{80} = \frac{80v}{80}

    0.5625 = v

    Hence, they moved at a velocity of 0.5625m/s

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