1. A child of mass m rides on a sled down a slick, ice-covered hill inclined at an angle θ with respect to the horizontal.
Draw a sketch
Draw a free body diagram
Set Cartesian coordinates (make a smart choice)
Find all x and y components of all forces and the acceleration
Write down Newton’s Second Law for the components
Quiz
Hint: Remember, that normal force is always perpendicular to a surface

2. Draw a free body diagram
A child of mass m rides on a sled down a slick, ice-covered hill inclined at an angle θ with respect to the horizontal.
Draw a sketch
Draw a free body diagram
Set Cartesian coordinates (make a smart choice)
Find all x and y components of all forces and the acceleration
Write down Newton’s Second Law for the components x y N θ a W

3. F1 m θ F1
Acceleration?
Net force?

4. Non Equilibrium
You pull a suitcase across the floor by an applied force F. Find the acceleration of the suitcase and the normal force exerted on it by floor x y m
Draw a free body diagram W N
2. Set Cartesian coordinates F
a = ?
3. Find all x and y components of all forces and of the acceleration θ
4. Write down Newton’s Second Law for the components
Direction ?

5. ΣFx = max ΣFy = may Fcos θ = ma Fsin θ + N - mg = 0 F W N θ a = ?
Direction ? x y W N F ma x y W
-mg N F
Fcos θ
Fsin θ ma
Fcos θ = ma
Fsin θ + N - mg = 0

6. Three people are pulling on a ring in a "2-D" tug of war
Three people are pulling on a ring in a "2-D" tug of war. Shown is a "top view". No one is winning - the ring is sitting still.
What is the net force on the ring?
What is the T3

7. An object is lowered by a rope at a constant speed
An object is lowered by a rope at a constant speed. How does the tension T in the string compare with the weight "mg" of the object?
A: T=mg
B: T > mg
C: T < mg
D: Not enough information given.

8. No Homework

9. A child of mass m rides on a sled down a slick, ice-covered hill inclined at an angle θ with respect to the horizontal.
What is the acceleration of the child
What is the normal force exerted on the child by the sled
Draw a sketch
Draw a free body diagram
Set Cartesian coordinates (make a smart choice)
Find all x and y components of all forces and the acceleration
Write down Newton’s Second Law for the components
Quiz
Hint: Remember, that normal force is always perpendicular to a surface

10. A child of mass m rides on a sled down a slick, ice-covered hill inclined at an angle θ with respect to the horizontal.
What is the acceleration of the child
What is the normal force exerted on the child by the sled
Quiz x y N θ a x y N W
-mgsin θ
-mgcosθ ma
-ma W
mg sin θ = ma
N – mg cos θ = 0
a = g sin θ
N = mg cos θ