Answer: Option C For such questions, always look at the blocks as one single system and find the acceleration of the whole as one. That acceleration is the same for both blocks. Then apply free body diagram (the one with the unknown T and with the least number of forces acting), find the unknown T. Refer to this post for more examples of such questions (some involve friction) https://www.sgphysicstuition.com/post/finding-forces-on-multiple-bodies

Answer: Option A Once the water wave is produced, frequency of the wave remains constant even when it travels from deep to shallow or vice versa. Frequency depends on the source (i.e. the dipper which creates the ripples) Refer to the video explanation

Answer: Option D For total internal reflection TIR to occur, two conditions must be present: 1. light must be travelling from a optically denser medium towards an optically less dense medium. 2. the angle of incidence i is greater than the critical angle c Key things to take note: 1. The angles stated on the diagram are not angles of incidence. Angle of incidence is between the incident ray and the normal. 2. The diagram on the left is TIR as all the light is being internally reflected within the optical denser medium, which is the liquid. 3. The diagram on the right with refracted ray along the boundary, i.e. angle of refraction is 90 degrees, the angle of incidence now is also the critical angle of the liquid. Refer to the video explanation

Answer: Option A Refer to the video explanation

Answer: Option A Firstly, you need to know that at both pivot P and Q, there are normal contact forces acting upwards on the plank. 2 conditions for the plank to be in equilibrium: 1) Sum of clockwise moment = Sum of anticlockwise moment (POM) 2) Net force = 0N (i.e. total upward forces = total downward forces) To find the value of the normal force, you can choose to take pivot about either P or Q. If you take moment about P, the normal force at P will not be in the Principle of Moments equation Ma = Mc as the line of action of the normal contact forces at P passes through the pivot P, there is no perperdicular distance, hence no moment created. We can determine the value of the normal contact forces at Q. Once normal force at Q is found, you can use the concept net force = 0N to find the normal force at P straight away, which is faster.

Answer: Option D From the resultant force-time graph, from time to time 0 to t, there is a decreasing resultant force. Using Fnet = ma, as the Fnet decreases, the acceleration is decreasing. But note that decreasing acceleration does not mean speed is decreasing. It means the speed is still increasing, just that the increment is getting smaller per unit time. After time t, there is not resultant force, hence no acceleration. Since the object is already moving, it will continue to move at constant speed in a straight line. On the speed time graph, D fits the scenario.

Answer: Option A When there is current flowing through the wire, there is magnetic field generated around the wire. To determine the direction of the magnetic field, we can use Right Hand Grip Rule (RHGR). To help in the visualisation, we can also use the ‘dot’ and ‘cross’ to represent magnetic field coming out of the paper and into the paper respectively.

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.

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.

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.

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.

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.