P10 Force and Motion

Question 1

What is Newton’s Second Law of Motion?

Answer 1

the acceleration of an object is:
- PROPORTIONAL to its DIRECTION,
- INVERSELY PROPORTIONAL to the MASS of the object.

Question 2

what is inertia?

Answer 2

the tendency of an object to stay at rest or continue in uniform motion

Question 3

what is the resultant force on an object falling in fluid?

Answer 3

its weight minus the frictional force on it

Question 4

why does the acceleration of an object decrease as it falls?

Answer 4

because frictional force on the object increases
as it speeds up

Question 5

what is terminal velocity?

Answer 5

when the frictional force on an object is equal and opposite to its weight
resulting in constant velocity

Question 6

the braking force needed to stop a moving vehicle from a fixed distance depends on:

Answer 6

• the speed it moves at,
• its mass.

Question 7

define stopping distance

Answer 7

the shortest distance a vehicle can safely stop in

Question 8

stopping distance formula

Answer 8

THINKING DISTANCE + BRAKING DISTANCE = STOPPING DISTANCE

Question 9

factors affecting braking distances

Answer 9

1. adverse road conditions (which increase braking distance to avoid slipping),
2. drugs, alcohol, distraction (which increase thinking distance)
3. faster vehicle (increases thinking and braking distance)
4. poorly maintained vehicles (less effective tyres/brakes increase braking distance)

Question 10

dangers of large decelerations

Answer 10

• brakes overheat,
• loss of control over vehicle.

Question 11

what is momentum?

Answer 11

momentum (kg m/s) = mass (kg) x velocity (m/s)

Question 12

what is the law of conservation of momentum?

Answer 12

the total momentum before and after an event in a closed system is equal

Question 13

what is the momentum of an object at rest?

Answer 13

0
because its velocity is 0

Question 14

how do crumple zones reduce the force of an impact?

Answer 14

increase impact time
reducing the change of momentum per second
decreasing force of impact
(reduce momentum at front, increase at back)

Question 15

what is impact force?

Answer 15

change of momentum per second

Question 16

describe the forces that two vehicles would each exert onto each other during a collision
in which no external forces act

Answer 16

exert equal and opposite forces onto each other
creating a total momentum equal to how it was before the collision

Question 17

how does a safety helmet reduce the force of an impact?

Answer 17

increases the impact time
reducing the change of momentum per second
reducing the force of impact

Question 18

how does a seat belt reduce the force of an impact

Answer 18

increases the impact time
reducing the change of momentum per second
and spreads out force across body
reducing the force of impact

Question 19

what does it mean for an object to be elastic?

Answer 19

it returns to its original shape
when the forces deforming it are removed

Question 20

what is Hooke’s Law?

Answer 20

the extension of a spring
is directly proportional to the force applied to it
until the limit of proportionality is exceeded
F = ek

Question 21

what happens to a string when its limit of proportionality is exceeded?

Answer 21

it becomes inelastically deformed
so when the weight is removed from it
it retains its extension