# Review: Newtons second Law or Solving Problems: (1)Isolate the object of interest (2)Sketch forces acting on object – indentify all the external forces.

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Review: Newtons second Law or Solving Problems: (1)Isolate the object of interest (2)Sketch forces acting on object – indentify all the external forces acting on an object. (3) Choose coordinate system (x &y) (4) Resolve into components Apply 2 nd law to each components. In components

m=2kg Ex. m=2kg Find the acceleration

5-4 Newtons third law of motion force hand exerts on box force box exerts on hand

Canoe Problem 1 2 m 1 =150kg m 2 =250kg 46N Ex. 2 boxes 10kg & 5kg, both are pushed in +x direction with a force of 20N, what is the force of contact? 20N 10kg 5kg F 12 F 21 (a) Find acceleration of each canoe? (b) what is the separation of canoes after 1.2 s?

5-5 The Vector Nature of Forces: Forces in Two Dimensions θ Review: F 1x= F 1 cosθ F 2x =F 2 F 1y =F 1 sinθ F 2y =0

Ex. Say dog 1 wants to go 32 0 north of east 12N, and dog 2 goes east 16N. Find magnitude and direction of accelerate? F 2 =16N x m=2kg F 1 =12N y

5-6 Weight Weight: force exerted on object by gravitational pull of earth. y a y =g W=mg Unit: N

Ex. 81 kg person has a weight ? Ex. What is the acceleration of the mass? F=200N 8kg

5-7 Normal forces Normal force: ; force exerted by table on object y

Problem: (a)What is the normal force exerted on the mass? (b)Find the acceleration of the mass? 30 0 8N 10kg

Ice Block Ex 5-8 F 1 =13N; F 2 =11N; m=6kg (a)Find the acceleration of ice box? (b)Find the normal force? 30 0 60 0 F2F2 F1F1

Apparent weight m=80kg what is the reading on the scale of elevator is going up at 3.2 m/s 2

Ex. Sliding down an incline, mass m, (neglect friction), find acceleration and normal force? N W α y x

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