Measurement
What instrument is used to measure the thickness of paper accurately?
Micrometer screw gauge
Hai Fang walks 3 m to the East followed by a 7 m to the West.
Find the displacement.
displacement = 7m - 3m
displacement = 4 m to the West
Describe the Newton's first law of motion.
Object remains its motion (at rest or moving in uniform speed), unless acted upon by an external force.
Three ways of transferring heat energy.
Conduction, convection and radiation
What is a longitudinal wave?
The vibration of particles is parallel to the direction of the wave propagation.
Name two scalar quantities and two vector quantities.
Scalar: Distance, speed, energy, temperature
Vector: Displacement, velocity, acceleration, forces
Dunmin walks 1.5 km from his house to school. The total time taken for the journey is 25 minutes.
Calculate his speed.
speed = 1500 / 1500
speed = 1 m/s
A car with a mass of 1500 kg is accelerating at 2 m/s2. Given that the driving force of the car is 4000 N.
Calculate the frictional force.
4000 - Ff = 1500 * 2
Ff = 4000 - 3000
Ff = 1000 N
Describe convection.
Cooler particles are denser and will sink to the bottom while the warmer particles are less dense and rise to the top. The continuous circulation of particles create convection current.
Two examples of transverse waves.
Any EM.
Describe how to find the volume of an irregular shape rock.
1. Add water to a displacement can (Eureka can or measuring cylinder) and record the volume.
2. Put the rock gently into the can and measure the total volume.
3. Substract the volume of water with the total volume of water with rock.
Describe terminal velocity.
At first, accelerating at 10 m/s2, then decreasing acceleration as the object gained air resistance (due to the increase in the falling velocity).
Eventually, falling at a constant velocity.
Air resistance = Weight of the object
State the principle of conservation of energy.
Energy cannot be created or destryed, it can transferred from one form to another.
Why a metal is a good conductor of heat?
Heat can be transferred through the lattice vibration and the movement of free electrons.
What is refraction of light?
The bending of light when passing through two different media with different optical density, due to the changing in speed and direction.
2000 nm converts to km.
2.0 x 103 x 10-9 x 10-3 = 2.0 x 10-9 km
A stone is thrown vertically upwards with an initial speed of 20 m/s.
Calculate the maximum height reached.
v² = u² + 2as
0 = 20² + 2(-10)s
0 = 400 - 20s
s = 400 / 20 = 20 m
An object with a mass of 20 kg is dropping from a height of 20 m. Calculate its maximum speed before it reaches the ground. [ignore air resistance]
KE = GPE
0.5 x m x v2 = mgh
v2 = 2gh
v2 = 2x10x20
v = 20 m/s
2kJ of heat energy is absorbed by 500g a metal. Given that the specific heat capacity of the metal is 400 J/kg oC. Calculate its final temperature. Take the initial temperature of the metal= 20oC.
change in temp = E/ m x c
change in temp = 2000 / 0.5 x 400
change in temp= 10oC
final temp = 20 + 10 = 30oC.
The light is travelling from the air to a glass.
Assume that the speed of light in the air is about 3 x 108 m/s. Calculate the refractive index of the glass if the speed of light in glass is 1.5 x 108 m/s.
n = 3/1.5
n = 2.0
A man is lifting a weight of 2000N to a vertical height of 1.5 m. Given that the man spent 0.8 s for the lifting, calculate the useful power by the man.
P = w/t
P = (2000 * 1.5)/ 0.8
P = 2400 W
A 2 kg block of metal is heated from 25°C to 75°C. The specific heat capacity of the metal is 500 J/kg°C.
How much heat energy is required?
Q = mcΔθ
= 2 kg × 500 J/kg°C × (75°C - 25°C)
= 2 × 500 × 50
= 50,000 J
A water wave has a wavelength of 0.5 m and a frequency of 4 Hz.
What is the speed of the wave?
Wave speed, v = f × λ
= 4 Hz × 0.5 m
= 2 m/s