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?

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