Newtons Laws
An object at rest remains at rest, and an object in motion remains in motion at constant velocity unless acted upon by a net external force.
Newton's First Law
What force acts downward on an object near Earth's surface?
Fg
friction acts on an object that is sliding across a surface
Kinetic friction.
A 50 N force acts at 30∘ above the horizontal. What equation would you use to find its horizontal component?
Fx=Fcos0
For an object on an incline, what component of gravity acts parallel to the surface
gx=Fgsin0
A 5 kg object experiences a net force of 20 N. What is its acceleration?
4 m/s^2
A box sits motionless on a horizontal table.
Fg (Downward) FN (Upward)
used to calculate kinetic friction
fk=Muk*FN
A 40 N force acts at 60∘ above the horizontal. What is its horizontal component?
20N
component of gravity acts perpendicular to an incline
gy=Fgcos0
A student pushes against a wall with a force of 100 N. What force responds?
Normal Force
A box is pulled to the right across a rough horizontal surface at constant velocity. Name the four forces acting on the box.
Check Drawing
A 10 kg box slides across a horizontal surface with μk=0.30. What is the friction force?
29.4N
A 50 N force acts at 30∘ above the horizontal. What are its horizontal and vertical components?
Fx=43.3N and Fy=25N
A 10 kg box rests on a frictionless 30∘ incline. How much of the component of gravity is pulling the box down the incline?
49N
A 10 kg box is pushed with a 50 N force to the right while friction acts with a 20 N force to the left. What is the acceleration of the box?
3 m/s^2
A 20 kg box is pulled upward with 80 N while drag acts with 30 N.
Check Drawing
A 20 kg box is pushed with 100 N but does not move. If the coefficient of static friction is 0.40, how much force does it take to move the box?
Greater than78.4N
A 20 kg box is pulled by a 100 N force at 30∘ above the horizontal. What is the normal force if the box remains on a horizontal surface?
FN=146N
A 10 kg box slides down a frictionless 47degree incline. What is its acceleration?
7.17 m/s^2
A 4 kg object accelerates at 6 m/s^2 to the right. Two horizontal forces act on it: 35 N to the right and an unknown force to the left. What is the magnitude of the unknown force?
11N
A 12 kg box is pulled across a horizontal surface by a 70N force directed 40degree angle.
Check
A 15 kg box is pulled horizontally with 75 N. The coefficient of kinetic friction is 0.20. What is the acceleration?
3.04 m/s^2
A 20.0 kg mass is suspended at rest by two cables. The left cable makes an angle of 37° above the horizontal, and the right cable makes an angle of 46° above the horizontal.
T1= 137.2N T2=157.7N
A 10 kg box slides down a 22∘ incline. The coefficient of kinetic friction is 0.20. What is the acceleration of the box?
1.85 m/s^2