Forces

Question 1

Explain the difference between scalar and vector quantities and contact and non contact forces

Answer 1

Vector quantities have a magnitude and direction, scalar quantities only have magnitude
When two objects have to be touching for a force to act, the force is a contact force, if the objects do not need to be touching it is a non contact force

Question 2

What is the formula for calculating the weight of an object

Answer 2

Weight(N)=Mass(kg) x gravitation field strength (N/kg)

Question 3

What is a free body diagram

Answer 3

A free body diagram shows all the forces acting on an object by using arrows to show the direction and relative magnitudes of the forces.

Question 4

Give the formula for calculating the work done by a force and explain what each symbol means

Answer 4

Work done (J)=Force(N) x Distance(M)

Question 5

How many joules of work does one Nm equal

Answer 5

1 Joule

Question 6

Describe the forces acting on an object in equilibrium

Answer 6

All the forces are balanced to give a resultant force of 0

Question 7

What is the difference between an elastic and an inelastic deformation?

Answer 7

An elastic deformation will return back to it’s original shape, an inelastic deformation won’t

Question 8

Give the equation that relates force, extension and the spring constant of an object

Answer 8

Force(N)=Spring constant(N/m) x extension (m)

Question 9

What is the limit of proportionality

Answer 9

The maximum force above which the graph curves showing extension is no longer proportional to the force

Question 10

How do you find the following from a linear force-extension graph: spring constant and work done

Answer 10

The gradient of the line is equal to the spring constant.
The energy in the elastic potential store is equal to the area under the force extension graph up to the limit of proportionality

Question 11

Give the equation used to find the energy in an elastic object’s elastic potential energy store

Answer 11

Elastic potential energy (J)=1/2 x spring constant(N/m) x Extension^2(m)

Question 12

Define a moment and state an equation for calculating the size of a moment

Answer 12

A moment is the turning effect of a force.

Moment(Nm)=Force(N) x distance from pivot(m)

Question 13

If a seesaw is balanced what can you say about it’s components

Answer 13

The anti clockwise moment is equal to the clockwise moment

Question 14

State an equation for calculating the pressure at the surface of a fluid.

Answer 14

Pressure(Pa)=Force(N)/Area of surface(m^2)

Question 15

Explain why the pressure increases as you go deeper into a column of a liquid

Answer 15

As the depth of the liquid increases, the number of particles above that point increases. The weight of these particles adds to the pressure felt at that point.

Question 16

What causes an object to float

Answer 16

When an object is submerged in a fluid pressure is exerted wth a resultant force upwards known as upthrust. The upthrust is equal to the weight of fluid that has been displaced. If an object’s weight is equal to the upthrust the force balance and the object floats.

Question 17

Explain how and why atmospheric pressure varies with height

Answer 17

As the altitude increases the atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface. There are also fewer air molecules above a surface meaning the weight of the air above it decreases.

Question 18

What is the difference between displacement and distance

Answer 18

Distance is a scalar quantity so doesnt involve direction. Displacement is a vector quantity measuring distance and direction in a straight line form an object

Question 19

Define acceleration in terms of velocity and time

Answer 19

Acceleration is the change in velocity in a certain amount of time

Question 20

What does the term uniform acceleration mean

Answer 20

Uniform acceleration means a constant acceleration

Question 21

What does the gradient represent for a distance time graph and a velocity time graph

Answer 21

The gradient in a distance time graph means speed. The gradient in a velocity time graph means acceleration

Question 22

What is terminal velocity and what causes it

Answer 22

Terminal velocity is the maximum speed an object can reach at a steady speed. At first speed is much higher than drag but as speed increases (acceleration) drag increases until the forces are balanced and the object travels at a constant speed.

Question 23

State Newton’s three laws of motion

Answer 23

Newtons first law:A resultant force is needed to make something start moving, speed up or slow down
Newtons second law:A force to be equal to change in momentum per change in time. Force and the acceleration are directly proportional and acceleration is inversely proportional to the mass of an object.
Newtons third law:When two objects interact the forces they exert on each other are equal and opposite.

Question 24

What is inertia

Answer 24

Until acted upon by a resultant force, objects at rest stay at rest and objects moving at a steady speed will stay moving at that speed.

Question 25

State the formula used to calculate an object’s momentum

Answer 25

Momentum (kg m/s)=Mass(kg) x Velocity(m/s)

Question 26

Explain how car safety features use momentum and forces to reduce the risk of injury to passengers

Answer 26

Cars are designed to slow people down over a longer time as the longer it takes for a change in momentum the smaller the rate of change of momentum and the smaller the force. Eg, crumple zones, seat belts stretch, airbags