Newton's Laws
State Newton's First Law
•An object in motion stays in motion and an object at rest stays at rest unless acted on by a net external force.
Draw the forces acting on a book resting on a table.
Gravity downward, normal force upward.
Write the formula for kinetic friction.
Fₖ = μₖN.
What is the x-component of a force F at angle θ?
Fₓ = F cos θ.
A block moves at constant velocity. What is ΣF?
0N
A 5 kg object experiences no net force. What is its acceleration?
0 m/s² because ΣF = 0 → a = 0.
Identify all forces on a sled being pulled by a rope.
Gravity, normal, tension, friction
A 10 N friction force acts on a sliding block with μₖ = 0.2. Find FN.
50N
A 20 N force at 30° to horizontal—find vertical component.
10N
A 2 kg mass accelerates at 6 m/s². Find net force.
12N
Explain the difference between mass and weight.
Mass refers to how much matter an object is made of. Weight is the force of gravity on an object.
A block resting on an incline is subject to three main forces. Name them.
Static friction prevents motion. True or false?
False, it prevents slipping/sliding.
Parallel: mgsinθ
Perpendicular: mgcosθ
Friction is 5 N opposite motion, applied force is 20 N. Find acceleration of 3 kg block.
ΣF = 20 - 5 = 15 N → a = 15/3 = 5 m/s²
A car accelerates at 3 m/s² with a net force of 1500 N. What is its mass?
500 kg
Why is normal force not always equal to mg?
Could be on an incline, or have other vertical forces pulling.
A 4 kg box on a floor has μₖ = 0.1. Find friction force.
3.92N
A rollercoaster vehicle has a mass of 500kg when fully loaded with passengers. If the vehicle has a speed of 20m/s at the lowest point of a dip, what is the force of the track on the vehicle at this point? r = 10m
24900N
Two blocks connected: 2kg and 1kg pulled by 18 N, friction negligible. Find acceleration.
a = F/m_total = 18 / 3 = 6 m/s²
Describe Newton’s Third Law with an example.
For every force, there is an equal and opposite reaction force. Examples may vary.
Find the tension in a 1m long string at the bottom of a vertical circle, while spinning a 4kg object. It takes 1/2 of a second to go through one full rotation.
671N
Explain the difference between μₛ and μₖ.
μₛ > μₖ; static friction prevents sliding, kinetic friction acts during sliding.
An object is hung from a cable with a mass of 3kg. The cable bends to create a 300 with the horizontal. What is the tension in the cable?
29.4N
An object in freefall with drag eventually reaches terminal velocity. Explain why.
Drag increases until it eventually equals weight. -> Net force = 0