Newton’s Second Law of motion (牛頓運動第二定律) Ch.8 Newton’s Second Law of motion (牛頓運動第二定律)

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100 N 200 N 100 N + 200 N = 300 N Left 5

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300 N 400 N 300 N + 400 N = 700 N North 7

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100 N 250 N -100 N + 250 N = 150 N Right 9

500 N 300 N 500 N - 300 N = 200 N South 11

200 N 300 N 500 N 500 N - 300 N – 200 N = 0 no direction

Newton’s 2nd Law of Motion

F = 100 N

F = 100 N a = F  m = 100  20 = 5 m s-2

F = 100 – 40 = 60 N

F = 100 – 40 = 60 N a = F  m = 60  20 = 3 m s-2

Thrust = Drag Lift = Weight It is because the aeroplane is moving at constant velocity means acceleration = 0 , i.e. the resultant force = 0.

Thrust > Drag It is because a resultant force in forward direction is acting on the aeroplane.

R F = 0 R = W = 650 N W

F = ma = (65) (2) = 130 N R’ – W = ma R’ = W + ma = 650 + 130 = 780 N

F = ma = (65) (-2) = -130 N R” – W = ma R” = W + ma = 650 + (-130)

F = 0 It is because the trolley is moving with constant velocity means acceleration = 0. (friction = 100 N)

F = 200 N

F = 200 N a = F  m = 200  25 = 9 m s-2

F = 200 – 100 – 100 (friction = 100 N) = 0  a = F  m = 0 200 N