Which speed-time graph represents the resultant-time graph?

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.

https://youtu.be/5BPXP3c_d_Q?si=Lfqnz90OKaLAnT1k

Two current-carrying wires perpendicular to each other, which region has the strongest magnetic field out of paper

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.

https://youtu.be/J_lPFWILCbg?si=wjAd_2As-VCFXal2

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.

Which types of radiation do the source emit by analysing count rate with different materials https://youtu.be/BrBpNYUplk8