4.1b Notes – Calculations using Net force and Newton’s 2 nd Law

1. 4.1b Notes – Calculations using Net force and Newton’s 2nd Law

2. Objectives • Interpret motion diagrams • Apply Newton’s Second Law of Motion to real life situations. • Solve calculation problems using Newton’s Second Law of Motion.

3. Calculating Net Force • Draw the picture in your notes • How do we calculate net force?

4. Example • Net Force = __________

5. Examples • Net Force = _________

6. Examples • Net Force = __________

7. Newton’s 2nd Law CalculationsF = ma • Determine the acceleration that result when a 12-N net force is applied to a 3-kg object and then to a 6-kg object. A 3-kg object experiences an acceleration of 4 m/s/s. A 6-kg object experiences an acceleration of 2 m/s/s.

8. Newton’s 2nd Law CalculationsF = ma • A net force of 15 N is exerted on an encyclopedia to cause it to accelerate at a rate of 5 m/s2. • Determine the mass of the encyclopedia. Fnet = 15 N a = 5 m/s/s. m = F/a m = (15 N) / (5 m/s/s) m = 3.0 kg

9. Example • Find the acceleration of a 10kg object undergoing the motion indicated in the diagram. • Step 1 – find the net force • Step 2 - use F=ma equation

10. Newton’s 2nd Law CalculationsF = ma • Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is doubled, then what is the new acceleration of the sled? Answer: 3 m/s/s The original value of 2 m/s/s must be multiplied by 3 (since a and F are directly proportional) and divided by 2 (since a and m are inversely proportional)

11. Newton’s 2nd Law CalculationsF = ma • Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is halved, then what is the new acceleration of the sled? Answer: 12 m/s/s The original value of 2 m/s/s must be multiplied by 3 (since a and F are directly proportional) and divided by 1/2 (since a and m are inversely proportional)

12. In-Class Assignment/Homework • 4.1 b WKT