Forces

Question 1

Resultant force

Answer 1

Two or more forces acting on an object can be replaced by a single for with the same effect

Eg) <—200N 400N—> = —>200N

Question 2

Newton’s first law

Answer 2

If the resultant force acting on an object is 0, then its acceleration will be 0

Question 3

Newton’s second law

Answer 3

An object will accelerate if there is a resultant force. Acceleration is directly proportional to resultant force, inversely proportional to mass

Question 4

Newton’s third law

Answer 4

Forces on interacting objects are equal an opposite

Question 5

Distance time graphs

Answer 5

Speed (m/s) = distance (m) / time (s)
Gradient = speed

Question 6

Velocity time graphs

Answer 6

Gradient = acceleration
Area = distance

Question 7

Acceleration

Answer 7

Acceleration (m/s^2) = v-u (m/s) / time (s)

Question 8

Change in velocity

Answer 8

v-u^2 = 2 x a x d

Question 9

Gravitational field strength

Answer 9

g (N/kg) = weight (N) / mass (kg)

Question 10

Stopping distance

Answer 10

Stopping distance = thinking distance + breaking distance

Question 11

What does breaking distance depend on?

Answer 11

-road material
-weather
-friction

Question 12

What does thinking distance depend on?

Answer 12

-drugs
-alcohol
-tiredness

Average person has a reaction time of 0.7s

Question 13

Change in momentum

Answer 13

Force (N) = m x v-u / time

Question 14

Factors that decrease change in momentum

Answer 14

-seatbelts
-crumple zone

Question 15

Momentum

Answer 15

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

Question 16

Conservation of momentum

Answer 16

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

Question 17

Falling objects

Answer 17

Initially, there is a resultant force downwards as her weight is greater than the air resistance. She accelerates. The air resistance then increases as she accelerates so the resultant force decreases until it reaches zero and we have reached a constant velocity. This is called the terminal velocity

Question 18

Core practical - how the acceleration of an object is affected by the resultant force and mass

Answer 18

Resultant force
-independent variable = resultant force
-dependant variable = acceleration
-control variable = mass

Mass
-independent variable = mass
-dependant variable = acceleration
-control variable = resultant force