force and motion
Newton’s First Law of Motion says that an object will stay at rest or continue moving at a constant speed in a straight line unless a force acts on it.
What single word is used to describe this idea?
Inertia
In simple, everyday language, what is momentum?
How hard it is to stop a moving object
How much movement an object has because of its mass and speed
Pressure is the force acting on a surface. What is the formula for pressure in solids?
Pressure = Force ÷ Area
Chemists count tiny particles like atoms and molecules in a special way.
What name is given to the unit that means a fixed number of particles, similar to how “a dozen” means 12?
The mole = 6.022 x 1023 particles
What is the relative molecular mass (Mr) of methane, CH₄?
16 AMU
A trolley has a mass of 2 kg and accelerates at 4 m/s².
What is the magnitude of the resultant force acting on the trolley?
Use Newton’s Second Law:
F = m×a
F = 2×4
F = 8 Newtons
Momentum describes how difficult it is to stop a moving object.
What is the formula for momentum?
Momentum = mass × velocity
What is the formula for fluid pressure, and which three factors affect the pressure in a fluid?
Fluid pressure = density × gravitational field strength × depth
P=⍴gh
What is the mass of 1 mole of water (H₂O)?
18 g
A 2.0 mol dm⁻³ solution of hydrochloric acid (HCl) is made up to a total volume of 1.0 dm³. (Cl = 35.5 AMU)
How many grams of HCl does this solution contain?
Relative formula mass of HCl = 1+35.5
Mass = 2.0 × 36.5 = 73 g
73 g of HCl
A trolley has a mass of 2 kg and is moving at 1 m/s.
A resultant force of 10 N acts on the trolley in the same direction as its motion.
How fast is the trolley moving after 1 minute?
(Assume the force stays constant and there is no friction.)
301 m/s
Three objects are moving in a straight line.
Which would be hardest to stop?
A) A 0.75 kg football moving at 12 m/s
B) A 3.0 kg suitcase moving at 3.2 m/s
C) A 1.5 kg skateboard moving at 6.0 m/s
B 3 x 3.2 = 9.6 kg m/s
A block has a mass of 1 kg and rests on a flat surface.
The block exerts a pressure of 500 Pa on the surface.
Take g=10 N/kg
Calculate the area of contact between the block and the surface.
P = F/A
F/P = A
10 N/500 Pa = A
1/50 m2 or 0.02 m2
Water is broken down by electrolysis according to the equation:
2H2O → 2H2 + O2
If 36 g of water is used, what mass of oxygen gas will be produced?
2H2O → 1O2
36 g water = 2 moles ∴ 1 mole of oxygen
O = 16 AMU ∴
32 grams of O2
A carbohydrate contains only carbon, hydrogen, and oxygen.
Analysis shows that it has the following composition:
Carbon: 40%
Hydrogen: 6.7%
Oxygen: 53.3%
What is the empirical formula of this carbohydrate?
Assume 100 g of substance:
C: 40 ÷ 12 = 3.33
H: 6.7 ÷ 1 = 6.7
O: 53.3 ÷ 16 = 3.33
C 3.3 : H 6.7 : O 3.3
C 1 : H 2 : O 1
Empirical formula = CH₂O
A rocket has a mass of 500 kg.
Gas leaves the rocket engine with a mass of 10 kg and is accelerated backwards at 200 m/s².
What is the acceleration of the rocket?
(Assume no air resistance and ignore gravity.)
4 m/s2
A 2.0 kg trolley is moving in a straight line at 4.5 m/s.
It collides with a stationary 3.0 kg trolley.
After the collision, the two trolleys stick together and move off as one.
What is the final speed of the two trolleys?
9 kgm/s / 5 kg
Final speed = 9/5 m/s = 1.8 m/s
Two open containers hold different liquids.
Container A contains oil of density 800 kg m⁻³ to a depth of 1.2 m
Container B contains water of density 1000 kg m⁻³ to a depth of 0.96 m
Take g = 10 N/kg
Calculate the pressure at the base of each container.
Which container exerts the greater pressure?
A 800 x 1.2 x g = 8 x 12 x 10 x g = 960 x g
B 1000 x 0.96 x g = 10 x 96 x g = 960 x g
The pressure at the base of both containers is the same: 9600 Pa
At room temperature and pressure (RTP), what volume would 2 moles of oxygen gas (O₂) occupy?
48 dm3/litres
Sulfuric acid reacts with sodium hydroxide according to the equation:
H2SO4 + 2NaOH → Na2SO4 + 2H2O
A student has 250 cm³ of 2.0 mol/dm³ sulfuric acid.
What volume of 1.0 mol/dm³ sodium hydroxide solution is required to completely neutralise the acid? (hint use no. of moles = C x V)
C x V = no. of moles
2 x 0.25 = 0.5 moles of H2SO4
H2SO4 + 2NaOH
no. of moles/C = V
1 mole/1M = 1 dm3 of NaOH
An object has a mass of 5.0 kg.
Two forces act on the object at right angles to each other:
A force of 6.0 N acts horizontally.
A force of 8.0 N acts vertically.
Calculate the acceleration of the object.
2 m/s2
Two trolleys move towards each other on a straight, frictionless track.
Trolley A has a mass of 2 kg and is moving to the right at 4 m/s.
Trolley B has a mass of 1 kg and is moving to the left at 2 m/s.
The trolleys collide elastically and move off in opposite directions.
After the collision, trolley B moves to the right at 6 m/s.
What is the speed of trolley A after the collision?
(Give your answer and state the direction of motion.)
Initial momentum
Trolley A: 2×4=8
Trolley B: 1×(−2)=−2
Total initial momentum
8+(−2) = 6 kg m/s
Final momentum
Trolley B: 1 × 6 = 6
So trolley A must have 0 momentum after the collision.
Trolley A comes to rest (0 m/s)
A solid metal cube has a volume of 1.0 m³.
The top of the cube is 5 m below the surface of pure water, so the cube is completely submerged.
The density of water is 1000 kg/m³.
Take g = 10 N/kg.
Calculate the upward force (upthrust) acting on the cube.
Ptop = pgh = 1000 x 10 x 5 = 50,000 N
Pbottom = pgh = 1000 x 10 x 6 = 60,000 N
difference = 10,000 N
Magnesium reacts with hydrochloric acid to produce hydrogen gas.
Mg + 2HCl → MgCl2 + H2
In an experiment, 48 litres of hydrogen gas are released at room temperature and pressure (RTP).
What mass of magnesium must have reacted?
(Relative atomic mass of magnesium = 24)
48 g
A compound contains only carbon, hydrogen, and oxygen.
Its percentage composition is:
Carbon: 54.5%
Hydrogen: 9.1%
Oxygen: 36.4%
(a) Calculate the empirical formula of the compound.
Further analysis shows that the relative molecular mass (Mr) of the compound is 88.
(b) Determine the molecular formula of the compound.
Assume 100 g:
C: 54.5 ÷ 12 = 4.545
H: 9.1 ÷ 1 = 9.1
O: 36.4 ÷ 16 = 2.275
Divide by the smallest (2.275):
C: 4.54 ÷ 2.275 = 2
H: 9.1 ÷ 2.275 = 4
O: 2.275 ÷ 2.275 = 1
Empirical formula = C₂H₄O
(b) Molecular formula
Empirical formula mass:
(2×12) + (4×1) + 16 = 44
Multiplier = 88/44 = 2
C4H8O2