Physics 1Pr Jan 2020

Question 1

1kPa is how many Pa

Answer 1

1000Pa

Question 2

How many N in 1mN

Answer 2

0.001 N

Question 3

evolution of stars with higher mass than sun through its entire life cycle

Answer 3

• Dust star
• Proto star
• Main sequence
• Red supergiant
• Supernova
• Black hole / Neuronstar

Question 4

The student suggests that the ball (light plastic) will reach the ground with a speed that is less
than 16m/s because of air resistance.
Use ideas about forces to justify the student’s suggestion.

Answer 4

• ball has weight
• ball accelerates
• Drag force / air resistance increase while accelerate
• Resultant force decrease
• So acceleration decrease
• Forces balanced
• Terminal velocity

Question 5

Explain why the voltage across the LDR decreases when the resistance of the
LDR decreases.

Answer 5

• larger current means larger voltage across fixed resistor;
• total voltage remains constant

Question 6

Describe how to obtain ACCURATE MEASUREMENTS of the mass and the volume of the rock.

8Mp total

Answer 6

• DIsplacement method
• measure mass of rock with balance
• measure rock first
• wet rock weight more
• use Displacement can and measuring cylinder
• Eye level?
• Make sure rock completely submerged
• Put rock in gently

Question 7

Ionisation

Answer 7

Removal of electrons from an atom

Question 8

Why workers is safe when alpha radiator emits in same room

Answer 8

• Alpha cannot penetrate few cm of air

Question 9

Half life meaning

Answer 9

Time taken for half of unstable nuclei to decay

(or radioactivity/ balloon)

Question 10

Explain, in terms of PARTICLES , why the pressure of the air inside the glass jar decreases.

Answer 10

• wall further apart
• therefore lower frequency of collisions
• Average force of wall is lower
• lower force means lower pressure for same wall surface area

Question 11

Explain why the balloons start to expand when the rubber sheet is pulled down.

Answer 11

• pressure outside balloon is lower than inside
• pressure difference cause force
• force is outward on balloon
• force causes extension on balloon

Question 12

Methods of increasing the magnitude of the magnetic force on the wire.

Answer 12

• increase current by increasing voltage
• increase magnetic field strength by using stronger magnet

Question 13

Explain how the circuit could be changed to make the wire vibrate.

Answer 13

Use A.C instead of D.C as A.C current has alternating current direction