May the force be with you
Solutions to the problems
Equations
Elevators are ruined
Forces
100
This force keeps Slinky Dog together in the movie Toy Story!
What is spring force
100
The net force of a 60N force directed to the right and a 17N force directed to the left
What is 43N to the right
100
A physics book rests on a bookshelf near the window of the classroom. Write the Fnet equation
What is Fnet = Fn - Fg
100
An elevator is accelerating up, a person feels
Heavier
100
According to this law, acceleration is directly proportional to net force and inversely proportional to mass.
What is Newton’s Second Law of Motion?
200
This force results in a large acceleration on humans but a very small acceleration on the Earth
What is gravitational force
200
A 20 kg bucket hangs from a string. Determine the tension (g = 9.8 m/s2)
What is 196 N upwards
200
A person lays down on their inner spring mattress. Write the Fnet equation for the vertical component of the person.
Fnety = Felastic - Fg
200
An elevator accelerates up at 18 m/s2. A 75kg man would appear to weigh
2085N
200
An object's tendency to remain at rest or in motion unless acted by an external force.
What is inertia?
300
This upward directed force keeps a stoplight from falling on to your car and moves elevators!
What is tension
300
A 1000 kg car accelerates at a rate of 7 m/s2. The coefficient of friction between rubber and the road is 0.9. Determine the force exerted by the engine to move the car.
What is 7000 N
300
A 195kg piano on the ground cannot be pushed to the right by a person. What are the forces acting on the piano horizontally?
Fnet = Fpush - Fs
300
An elevator accelerates down at 18 m/s2. A 75 kg man appears to weigh
What is 615 N
300
State Newton's Second Law (formula at least)
Fnet = ma
400
Without this force, walking would be impossible
What is friction
400
When an objecting is falling due to gravity only.
What is free fall?
400
State Newton's First Law
Inertia
400
A 68 kg person stands on an elevator. The instant the elevator begins to move, the person feels 35 N heavier. What is the acceleration of the elevator.
0.51 m/s2
400
State Newton's Third Law
Action Reaction
500
This principle explains why astronauts experience weightlessness in orbit, even though gravity is still acting on them.
What is apparent weightlessness (normal force = 0 during free fall)?
500
Two masses, 8 kg and 12 kg, are connected by a light rope over a frictionless pulley. Calculate the acceleration of the system and the tension in the rope.
Acceleration:
Tension:
(or using the other mass: 
)
500
This equation combines gravitational force and acceleration to determine the apparent weight of an object in an accelerating elevator.
What is F = m(g ± a)?
500
A 60 kg person stands on a scale in an elevator accelerating upward at 3 m/s². Calculate the apparent weight shown on the scale.
What is 768 N?
(Solution: F = m(g + a) = 60(9.8 + 3) = 60 × 12.8 = 768 N )
500
A spring stretches 0.25 m when a 50 N force is applied. Calculate the spring constant and predict how far the spring will stretch if the force is doubled.
Spring constant:
If force is doubled (100 N):