IB physics forces, circular motion, momentum etc

A roller-coaster car goes through a vertical loop.

At which point does a passenger feel the "lightest"? (This corresponds to the point where the normal force on the passenger is at its minimum.)

Identify this point.

at the very top of the loop

A hockey puck slides on a sheet of frictionless ice at a constant velocity.

Identify the net force acting on the puck.

zero

A student is standing on a bathroom scale inside an elevator. The scale reading (their 'apparent weight') is greater than their true weight (fg=mg).

Identify the motion of the elevator that could cause this reading.

the elevator is accelerating upwards 

Two solid spheres of the exact same volume are fully submerged in water. Sphere 1 is made of lead (very dense) and Sphere 2 is made of aluminum (less dense).

Identify the correct statement about the buoyant force () acting on the two spheres.

The buoyant force is the same on both spheres.

In a car crash, an airbag inflates to cushion the driver, bringing them to a stop. The airbag does not change the total change in momentum (impulse) the driver experiences, which is determined by their initial mass and velocity.

The primary, life-saving function of the airbag is related to how it manages the forces involved during this impulse.

Identify the statement that correctly describes this primary function.

Increase the collision time (delta t) to decrease the average force (F) for a fixed change in momentum (delta p).

A car is driving in a circle at a constant speed of 20 m s^-1.

Identify the correct statement.

The car is accelerating because its velocity (a vector) is changing direction.

A book is resting on a horizontal table. The Earth exerts a downward gravitational force on the book, which is one half of a Newton's 3rd Law force pair.

Identify the other half of this force pair (the “reaction” force).

The upward gravitational force the book exerts on the Earth

A heavy box rests on a horizontal floor. The coefficient of static friction between the box and the floor is .

You push horizontally on the box with a force , but the box does not move.

Identify the magnitude of the static friction force, , acting on the box.

ff=fpush

ρ

density of fluid (kg m⁻³)

η

fluid viscocity (N s m⁻²)

μ_d

Coefficient of dynamic friction (unitless)

k

spring constant (N m⁻¹)

ω

angular velocity (rad s⁻¹)

F_N

normal force (N)

J

impulse (N s)

μₛ

coefficient of static friction (unitless)

p 

linear momentum (kg ms⁻¹)

T

period (s)

In physics, Newton's Second Law is often introduced as fnet=ma, but its more fundamental and general form is fnet=delta p/delta t.

Identify the primary reason why the momentum-based form is considered more fundamental.

fnet=delta p/delta t is more general because it correctly describes systems where mass is not constant, such as a rocket expelling fuel.

A car travels at a constant speed v and safely navigates a circular turn of radius r . The static friction force providing the necessary centripetal force is F.

The car now attempts to navigate the same turn (same radius r ) at triple the speed (3v).

Identify the new centripetal force required to make the turn at this higher speed.

9F

A block rests on a flat, horizontal board. The normal force on the block is FN and the gravitational force on it is Fg. At this point, FN=Fg .

You then slowly lift one end of the board, increasing the angle of inclination from 0° (horizontal) towards 90° (vertical).

Identify what happens to the magnitude of the normal force as the angle increases.

The normal force decreases (approaching zero)

A free-body diagram (FBD) is a critical tool used in physics to analyze the forces acting on a single object.

Identify the statement that describes the most important and fundamental rule for constructing a valid FBD.

It must show all forces acting on the object and only the forces acting on the object.

You are standing on a scale in an elevator that is accelerating downward, but not in freefall.

Identify the correct description for the reading on the scale (your "apparent weight") compared to your true weight.

Less than your true weight (mg)

Collisions between objects are categorized based on how kinetic energy is conserved. These categories include elastic, inelastic, and perfectly inelastic collisions.

Even when kinetic energy is lost to heat or deformation, one fundamental quantity remains constant for the system as a whole, provided the system is isolated from external forces.

Identify the quantity that is conserved in all types of collisions within an isolated system.

total momentum

Consider a perfectly inelastic collision between two objects in a closed system.

Identify the statement that must be true for this type of collision.

The objects stick together, and the maximum possible amount of kinetic energy is lost

An "explosion" describes a process where an object or system breaks apart. Common examples include a cannon firing a cannonball or two ice skaters pushing off each other. In this type of interaction, the system starts from rest and the parts move away from each other due to internal forces.

This process can be thought of as the reverse of a perfectly inelastic collision.

Identify the correct statement describing the conservation of momentum and the change in total kinetic energy (KE) for such an explosion.

Momentum is conserved, and total KE increases

An object is in uniform circular motion.

What is the correct definition of the term “centripetal force” (Fc)?

Identify the correct description.

It is the net force that points toward the center of the circle, caused by other forces like tension, gravity, or friction.

A car travels around a horizontal, unbanked circular track.

Identify the force responsible for providing the centripetal acceleration.

The force of static friction between the tires and the road