Forces and Motion

Question 1

Is distance a scalar or vector quantity?

Answer 1

scalar (no specific direction)

Question 2

If an object moves 3 metres left then 3 metres back to its original position, what is it’s total displacement?

Answer 2

• zero displacement
• displacement is a vector quantity so it also involves direction
• the object starts and ends at the same point

Question 3

State a typical value for the speed of sound

Answer 3

330 m/s

Question 4

What is a typical value for human walking speed?

Answer 4

1.5 m/s

Question 5

What is a typical value for human running speed?

Answer 5

3 m/s

Question 6

What is a typical value for human cycling speed?

Answer 6

6 m/s

Question 7

State the equation linking distance, speed and time

Answer 7

distance = speed x time

Question 8

Why can an object travelling at a constant speed in a circle not have a constant velocity?

Answer 8

• speed is a scalar quantity
• velocity is a vector quantity meaning it can only be constant if the direction is constant
• the direction is continually changing in circular motions

Question 9

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

Answer 9

the speed is equal to the gradient of the graph

Question 10

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

Answer 10

• draw a tangent on the curve at the required time
• calculate the gradient of the tangent

Question 11

State the equation for the average acceleration of an object

Answer 11

change in velocity / time taken

Question 12

How can the distance travelled by an object be calculated from a velocity-time graph?

Answer 12

it is equal to the area under the graph

Question 13

Give an approximate value for the acceleration for an object in free fall under gravity near Earth’s surface

Answer 13

9.8m/s

Question 14

What cane be said about the resultant force acting on an object when it is falling at terminal velocity?

Answer 14

• resultant force is zero
• when at terminal velocity, the object is moving at a constant speed and so isn’t accelerating

Question 15

State Newton’s first law for a stationary object

Answer 15

if the resultant force on a stationary object is zero, it will remain at rest

Question 16

State Newton’s first law for a moving object

Answer 16

if the resultant force on a moving object is zero, it will remain at a constant velocity

Question 17

What can be said about the braking and driving forces when a car is driving at constant velocity?

Answer 17

the braking forces are equal to the driving forces

Question 18

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

Answer 18

since there is a change in direction, there is a change in velocity and so there must be a resultant force

Question 19

What is inertia?

Answer 19

the tendency of an object to continue in its state of rest or uniform motion

Question 20

State the defining equation for Newton’s second law

Answer 20

resultant force = mass x acceleration

Question 21

State Newton’s second law in words

Answer 21

an objects acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass

Question 22

What is inertial mass?

Answer 22

• a measure of how difficult it is to change a given object’s velocity
• the ratio of force over acceleration

Question 23

What is the symbol used to represent an approximate value?

Answer 23

~

Question 24

State Newton’s third law

Answer 24

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

Question 25

What is the stopping distance of a vehicle equal to?

Answer 25

the sum of thinking and breaking distance