chapter 4 - forces

Question 1

name an instrument which can be used to measure force

Answer 1

spring balance

Question 2

name the 4 ways in which a force may change the motion of a body

Answer 2

1. move a stationery object
2. increase the speed of a moving object
3. slow down or stop a moving object
4. change the direction of a moving object

Question 3

state newton’s first law

Answer 3

an object at rest will remain at rest and an object in motion will continue in motion at constant velocity in the absence of a resultant force acting on it

Question 4

state newton’s second law

Answer 4

when a resultant force acts on an object of constant mass, the object will accelerate in the direction of the resultant force

Question 5

formula for calculating resultant force

Answer 5

FR = ma

(mass x acceleration)

Question 6

state newton’s third law

Answer 6

if object A exerts a force F AB on object B, then object B will exert an equal and opposite force F BA on object A

Question 7

definition of inertia

Answer 7

inertia is the reluctance of an object to change its state of rest or motion due to its mass

Question 8

does inertia depend on mass?

Answer 8

yes

objects having a greater mass have a greater inertia

the greater the mass of a body, the more difficult it is to start it moving or to stop it

Question 9

what is the m/s2 of constant velocity

Answer 9

0m/s2

Question 10

state 2 positive effects of friction

Answer 10

1. we can walk without slipping
2. moving objects are able to slow down when needed

Question 11

state 2 negative effects of friction

Answer 11

1. cars are less efficient by up to 20%
2. moving parts in engines, motors and machines suffer wear and tear

Question 12

state the relationships between resultant force and acceleration

Answer 12

if resultant force increases, acceleration increases

if resultant force is constant, acceleration is constant

Question 13

state the relationship between speed, velocity, acceleration

Answer 13

if speed is constant, and velocity is constant, acceleration is zero

Question 14

effects of air resistance on falling object

Answer 14

1. opposes the motion of moving objects
2. increases with the speed of objects
3. increases with the surface area of objects
4. increases with the density of air

Question 15

how to calculate distance travelled from a speed time graph?

Answer 15

area under the graph

Question 16

factors affecting air resistance

Answer 16

1. shape of object
2. surface area of object

Question 17

description for decreasing acceleration

Answer 17

• moving with decreasing acceleration
• air resistance is acting upwards
• his weight is acting downwards on him
• air resistance increases with his falling speed, while his weight is constant
• the resultant force acting on the parachute will decrease
• since F=ma, when resultant force decreases, the acceleration will decrease