Physics - OCR Gateway P2

State the equation linking distance, speed and time.

Distance (m) = Speed (m/s) x Time (s).

How can speed be calculated from a distance-time graph?

Speed is equal to the gradient of the graph.

What must be done to calculate speed at a given time from a DT graph for an accelerating object?

Drawing a tangent to the curve at the required time, calculate the gradient of the tangent.

State the equation for the average acceleration of an object. Give appropriate units.

Acceleration (m/s^2) = (Change in Velocity (m/s))/(Time (s) taken).

How can the distance travelled by an object be calculated from a VT graph?

It is equal to the area under the graph.

What is a scalar quantity?

A quantity that only has a magnitude, a quantity that isn't dependent on direction.

What is a vector quantity?

A quantity that has both a magnitude and an associated direction.

How can a vector quantity be drawn and what does it show?

As an arrow, length of the arrow represents the magnitude, arrow points in the associated direction.

Is force a vector or a scalar quantity?

Vector, has both a magnitude and an associated direction.

Give three examples of vector quantities.

Velocity, displacement, force.

Give three examples of scalar quantities.

Temperature, time, mass, speed, distance.

How do you calculate average speed for non-uniform motion?

Average Speed (m/s) = Change in Distance (m) / Change in Time (s).

What piece of apparatus may be used to record the time taken for a very fast object to move a given distance?

Light Gates.

What is a force?

A push or pull acting on an object due to an interaction with another object.

What are the two categories that all forces can be split into?

Contact forces (objects touching), non-contact forces (objects separated).

Give three example of contact forces.

Friction, air resistance, tension.

Give three examples of non-contact forces.

Gravitational forces, electrostatic forces, magnetic forces.

What is the name given to the single force that is equivalent to all the other forces acting on a given object?

The resultant force.

State Newton's first law for a stationary object.

If the resultant force on a stationary object is zero, the object will remain at rest.

State Newton's first law for a moving object.

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction).

If an object changes direction but remains at a constant speed, is there a resultant force?

Since there is a change in direction there is a change in velocity and so there must be a resultant force.

When does an object fall with terminal speed?

When the upwards force (air resistance) and the downwards forces (weight) are equal to each other, no resultant force so constant speed.

What happens to the magnitude of air resistance on a falling object when the velocity increases?

As velocity increases, the force of air resistance on the object will also increase.

State the defining equation for Newton's Second Law.

Resultant force (N) = Mass (kg) x Acceleration (m/s²) F = ma

State Newton's Second Law in words.

An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.

What is inertia?

The tendency of an object to continue in its state of rest or uniform motion, in other words inertia is an object's resistance to motion.

What is inertial mass?

A measure of how difficult it is to change a given object's velocity, the ratio of force over acceleration.

State Newton's Third Law.

Whenever two objects interact, the forces that they exert on each other are always equal and opposite.

State the equation to calculate an object's momentum.

Momentum (kgm/s) = Mass (kg) x Velocity (m/s). P = mv.

What is the unit used for momentum?

kgm/s. Kilogram meters per second.

In a closed system, what can be said about the momentum before and after a collision?

The total momentum before = the total momentum afterwards.

State an equation linking change in momentum, force and time.

Force x Time = Change in momentum.

Explain how a seatbelt improves a passenger's safety during a collision.

The passenger must decelerate from the vehicle's velocity at impact to zero so they experience a force, this force = rate of change of momentum, seatbelts increase the time over which the force is applied, reducing the rate of change of momentum, therefore reducing force felt by passenger.

What quantity is equal to the force experienced in a collision?

The rate of change of momentum.

What does it mean if a force is said to do 'work'?

The force causes an object to be displaced through a distance.

What is the equation used to calculate work done?

Work done (Joules) = Force (Newtons) x Distance (meters).

Under what circumstance is 1 joule of work done?

When a force of 1N causes a displacement of 1m.

What is power?

The rate at which work is done. The unit is Watt (W).

What is one watt equal to?

one joule per second.

State the equation used to calculate power.

Power (W) = Work Done (J) / Time (s).

What can be said about the velocity of an object travelling in circular motion at constant speed?

Velocity is constantly changing since velocity is a vector and vectors depend on direction and magnitude and since direction is continually changing so does velocity.

Explain the relationship between the force applied and the extension of an elastic object.

Extension is directly proportional to force applied, provided that the limit of proportionality is not exceeded.

What is meant by an inelastic (plastic) deformation?

A deformation which results in the objectbeing permanently stretched, object doesn't return to its original shape when force is removed.

State the equation relating force, spring constant and extension.

Force (N) = Spring Constant (N/m) x Extention (m).

What is Hooke's law?

A law that states that the force applied is directly proportional to the extension of an elastic object.

At what point does Hooke's law no longer apply?

The limit of proportionality.

What does the limit of proportionality look like on an extension-load graph?

Where the graph stops being linear.

What type of energy is stored in a spring when it is stretched?

Elastic potential energy.

What can extension be replaced with in the equation for spring force?

Compression.

What is the equation for elastic potential energy?

Energy = ½ x Spring Constant (N/m) x (Extension)² (m).

What is weight?

The force that acts on an object due to gravity and the object's mass.

What is the unit used for weight?

Newton (N).

What is the unit used for gravitational field strength?

N/kg.

What is the equation used to calculate weight?

Weight (N) = mass (kg) x gravitational field strength (N/kg).

What is meant by an object's centre of mass?

The single point through which an object's weight can be considered to act through.

What type of field does all matter have?

Gravitational field.

How does the gravitational field of an object change as the object becomes more massive?

Field strength increases.

What letter is used to represent gravitational field strength and what is its value at the surface of Earth?

g. 10 N/kg.

What is the acceleration of an object falling in free fall with no resistive forces acting?

10 m/s^2.

Why would you weight be different if you were on a different planet?

Gravitiational field strength varies for each planet.

What piece of equipment can be used to measure an object's weight?

A calibrated spring-balance or newton-meter.

What is an alternative name for the turning effect of a force?

A moment.

State the equation used to calculate the moment of a force.

Moment of force (Nm) = Force (N) x Distance (m).

What distance measurement is used when calculating a moment?

The perpendicular distance from the pivot to the line of action of the force.

If an object is in equilibrium, what can be said about the moments acting on the object?

The clockwise moments are equal to the anticlockwise moments.

What does the direction of a resultant moment acting on an object tell you?

The direction that the object will rotate around the pivot point.

In any fluid, at what angle do the forces due to pressure act on a given surface?

At right angles (normal to) the surface.

What can be said about the pressure in a simple hydraulic system?

Pressure in the fluid is constant through the fluid (can't be compressed or expand).

Explain how a simple hydraulic lift works.

Pressure is constant in the fluid, force applied on each platform is equal to product of pressure and area (F = pA), one platform has a larger area than the other meaning force produced is greater than force applied to the smaller platform.