英文物理問題 四條

1. what will be the final velocity of a 5.0 g bullet starting from rest , if a net force 45 n is applied over a distance of 0.8 m?

2A. what is the net force nedded to lift a full grocery sack (weighing 210N)

2B.what is the net force needed to accelerate the grocery sack upward at 1.5 m/s^2

3.A car has a mass of 820 kg. It starts from rest and travels 41 m in 3.0 s.

What is the net force applied to the car?

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  • CK
    Lv 7
    7 年前
    最愛解答

    1. what will be the final velocity of a 5.0 g bullet starting from rest , if a net force 45 n is applied over a distance of 0.8 m?

    Work done = FS = (45)(0.8) = 36 J

    This energy changes to kinetic energy of bullet

    36 = (1/2) mV² = (1/2)(5/1000)V²

    V = 120 m/s

    2A. what is the net force nedded to lift a full grocery sack (weighing 210N)

    210 N is needed

    2B. what is the net force needed to accelerate the grocery sack upward at 1.5 m/s^2

    since F=mg ; 210 = m(10) ; (這裏,我用了 g=10 ,如果有需要改回 9.8 ,自己改啦)

    m = 21 kg

    The force that needed :

    F=ma = (21)(1.5) = 31.5 N

    3. A car has a mass of 820 kg. It starts from rest and travels 41 m in 3.0 s. What is the net force applied to the car?

    S = ut + (1/2)at²

    41 = 0 + (1/2)a(3.0)²

    a = 9.111 m/s²

    F = ma = (820)(82/9) = 7471 N

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