Basics
State Newton's First Law of Motion in words.
An object remains at rest or in uniform motion in a straight line unless acted on by an unbalanced external force.
For a box at rest on a horizontal table name the two vertical forces and their directions.
Weight 𝐹𝑊 acts downward, and the normal force 𝐹𝑁 acts upward.
Write the equation for the maximum static friction force in terms of μs and the normal force.
𝐹𝑓𝑠 max=𝜇𝑠𝐹𝑁
In an elevator accelerating upward is the scale reading less than equal to or greater than your actual weight FW?
Greater than FW
A 10.0 kg box is on a 30.0∘ ramp with 𝜇𝑘=0.20. It is pulled up the ramp at constant velocity by a rope parallel to the ramp. Find the normal force, friction force, and tension.
FW=98.1N; 𝐹𝑊⊥≈85.0N so 𝐹𝑁≈85.0N;
𝐹𝑓𝑘=𝜇𝑘𝐹𝑁≈17.0N down the ramp;
Constant velocity =>
T=FW∥+Ffk≈66.1N up the ramp.
What is inertia and which of Newton's laws is it most closely related to?
Inertia is an object's resistance to changes in its motion; it is most closely related to Newton's First Law.
A 5.0 kg mass hangs at rest from a vertical rope. What two forces act on the mass and what is the relationship between their magnitudes?
Weight acts downward and tension acts upward; their magnitudes are equal.
A 10.0 kg box rests on a horizontal surface. Find its weight and normal force.
Fw=98.1N downward
FN=98.1N upward
A 60.0 kg student stands on a scale in an elevator at rest. What does the scale read (to the nearest newton)?
590N.
A book rests on a table. Name a pair of Newton's Third Law forces in this situation.
The book pushes down on the table and the table pushes up on the book with an equal and opposite force.
A sled is pulled to the right by a rope while friction acts to the left. If the sled speeds up to the right which force is larger and why?
The pull to the right is larger than the friction to the left because the net force must be in the direction of the acceleration.
A 5.0 kg box moves on a horizontal surface with 𝜇𝑘=0.30. The normal force is 49 N. Find the kinetic friction force.
15N opposite the direction of motion
A 5.0 kg block is on a frictionless 30∘ ramp. What is its acceleration down the ramp?
4.9m/s2 down the ramp.
A 2.0 kg object experiences a net force of 10. N to the right. What is its acceleration?
5.0m/s2 to the right.
A horizontal 12. N force acts to the right and a 7.0 N force acts to the left on a cart. Determine the magnitude and direction of the net force.
5.0N to the right.
Explain the difference between static friction and kinetic friction.
Static friction acts when surfaces are not sliding and can be anywhere from 0 to a maximum value; kinetic friction acts when surfaces are sliding and has a constant magnitude for a given normal force.
A 10.0 kg block rests on a frictionless 37∘ ramp. Find the normal force on the block.
FN≈78N.
A box moves at constant velocity on a horizontal surface. What can you say about the net force on the box and the individual forces acting on it?
The net force is zero, and all forces balance (for example, friction equals the applied force, and the normal force equals the weight).
A 6.0 kg mass hangs at rest from two ropes from the ceiling. Is the tension in each rope greater than, less than, or equal to the weight of the mass?
The tension in each rope is greater than half the weight; the vertical components of the two tensions add to equal the weight.
A 20.0 kg box is pulled with an 80. N horizontal force on a surface with 𝜇𝑘=0.20. Find the acceleration.
2.04m/s2 to the right
A 70.0 kg student in an elevator has a scale reading less than FW. What does this tell you about the direction of the elevator's acceleration?
The elevator is accelerating downward (or moving upward while slowing down).