Topic 5 - Forces and Materials (GCSE Edexcel CombinedPhysics Retrieval Questions)

How can you resolve vectors?

By drawing scale diagrams.

Why does is an object travelling in a circle at a constant speed accelerating?

Because it is changing direction, so its velocity is changing.

"What is the definition of centripetal force?

The resultant perpendicular force towards the centre of the circle required to keep a body in uniform circular motion.

Give the equation linking momentum, mass and velocity?

momentum = mass x velocity

What is the unit of momentum?

kgm/s

Is momentum a scalar or vector?

vector

What is an elastic collision?

Kinetic energy is conserved

What is an inelastic collision?

Kinetic energy is not conserved.

What is the principle of conservation of momentum?

In a closed system, the total momentum before a collision is equal to the total momentum after the event.

Give the equation linking force, change in momentum and time.

Force = change in momentum/time

Define inertia.

The tendency of an object to continue in its state of rest, or in uniform motion unless acted upon by an external force

Define inertial mass.

The property of an object which describes how difficult it is to change its velocity

How does a seatbelt reduce injuries?

They increase the time taken for the car and passengers to slow down, and so reduce the forces involved.

Define stopping distance.

Stopping distance = Thinking distance + Braking distance

How does stopping distance vary with speed?

The greater the speed of the vehicle, the greater the stopping distance

Why can breaks overheat?

The kinetic energy of the vehicle is converted to thermal energy of the brakes.

Define reaction time.

A measure of how much time passes between seeing something and reacting to it.

What is the average human reaction time?

In the range of 0.2 - 0.9 seconds

What affects braking distance?

Speed, Vehicle Conditions, Road Conditions, Vehicle Mass

What affects thinking distance?

Speed, Reaction Time (Tiredness, Distractions, Intoxications)

What is elastic distortion?

When objects return to their original shape when the stretching force is removed

What is inelastic distortion?

When objects remain stretched and do not return completely to their original shape even when the stretching force is removed

Define Hooke's Law.

The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

What is the limit of proportionality?

The point beyond which the relationship between force and extension is no longer directly proportional

Give the equation linking force, spring constant and extension.

Force = spring constant x extension

What is the unit for spring constant?

Newtons/meter (N/m)

How is the spring constant related to stiffness?

The higher the spring constant, the higher the stiffness

Define elastic potential energy.

The energy stored in an elastic object when work is done on the object

Give the equation linking elastic potential energy, spring constant and extension.

Elastic Potential Energy = 0.5 x spring constant x extension²