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- Which types of radiation do the source emit by analysing count rate with different materials
Answer: Option D Alpha emission is the least penetrating, easily be blocked by a few cm of air, skin or thin paper. Beta emission can be blocked by a few cm of aluminium. Gamma emission can be blocked by a few cm of lead or metres of concrete. Refer to the video to understand how to apply the concepts.
- Energy COE - Bullet in tree trunk, find the frictional force in stopping the bullet
Answer: Option C With first glance, we may think of using kinematics to solve. It can, but the process will be longer. Refer to the video towards the end. For such questions, it will be much easier to use conservation of energy (COE). Besides the usually equating KE to GPE, we must not forget that we can also equate KE to WD. All are energy.
- Which statement describes an electrical source of 5V?
Answer: Option B Emf is the work done (energy needed) to carry a unit charge (1C) through the whole complete circuit. By definition, it is with respect to a unit charge (1C). In general, it can also mean what is the emf when a certain amount of energy is carry certain amount of charge round the complete circuit. Using V = E/Q, as long as the V is 5V, it is correct. Note that 1C is NOT 1 electrons. The amount of charge on an electron is about 1.6 x 10^-19 C. So there are many electrons in 1 C.
- Wavefront with point X and Y on trough and crest respectively
Answer: Option B Wavefront is an imaginary line that joins all identical adjacent points that are in phase. So if you assume the circular wavefront that connects Y is crest, than X will be a trough.
- Weight-mass graph - Find g on different planets
Answer: Option A W = mg, where g is the gravitational field strength. g = W/m, hence g is the gravitational force (pull) acting per unit mass of an object. In addition, in the weight-mass graph, the gradient represents the g. I.e the steeper the line, the higher the g for the planet. Mass is the amount of matter in the body. So for this question, it is important to know that mass remains constant whether it is on planet P or Q.
- Displacement-time graph and Velocity time graph of a ball thrown and comes down - Part 03
When a ball is thrown up and it comes down, the motion varies. This video will cover how the various graphs are sketched and why. View the two related videos below
- Displacement-time and Velocity-time graph when ball is dropped and it rebounces (no energy lost) - Part 01
When a ball dropped and then it re-bounces, the motion varies. This video will cover how the various graphs are sketched and why. In this ideal situation, you ignore air resistance and assume no energy converted to other forms as the ball hits the floor. View the two related videos below
