Physics Notes Newton’s 2nd Law – Basics

NOTES Newton’s 2nd Law

Net Force and Resultant

Example

 

YOUR TURN! Scifo the skater has a total mass 25 kg and is propelled by rocket power (FR).

ROCKET FORCE

(N)

FRICTION FORCE

(N)

FORCE DIAGRAM

NET FORCE (N) AND DIRECTION ACCELERATION (m/s2)

100N 0N

200N 0N

_______ 0N

10 m/s2

(HINT: Work backwards…Use ΣF=ma to solve for Force)

100N 50N

200N 50N

_______ 50N

10 m/s2

(HINT: Work backwards…Use ΣF=ma to solve for Force)

 

KEEP GOING!

1. Force diagrams are shown for a variety of physical situations. Use Newton’s Second Law of

motion (Σ𝐹 = 𝑚 ∙ 𝑎) to fill in all the blanks. Remember that the gravitational field strength (𝑔) is

9.8 N/kg in our gravitational force equation (𝐹! = 𝑚 ∙ 𝑔).

 

1. Gravity! Draw a force diagram for a 10 kg ball falling with no air resistance. What is the acceleration of the ball?

2. Gravity! Draw a force diagram for a 50 kg ball falling with no air resistance. What is the acceleration of the ball?

3. A little more challenging. A 2 kg bucket is at the bottom of a 9 m deep well and is initially at rest. The bucket is then pulled to the top of the well by a string that exerts a constant tension force, such that it reaches the top in 3 seconds. During this interval, what is the tension force in the string?

4. A little more challenging. For Thanksgiving Mom lifts a 20.0 lb turkey (1 kg weighs 2.20 lb) from the lower part of the fridge to the countertop. Find the force Mom exerts for each part of the turkey's trip: (a) Initially accelerating the turkey from rest at 1.00 m/s2, straight upward. (b) Moving the turkey upward at a constant 0.50 m/s. (c) Slowing the turkey to a stop 1.00 m/s2