4 physics HKCEE MC

Q1: the power is measued in Js^-1 but not Jmin^-1.You should subsitute t=5x60 but not t=5.

Q2: the answer is not D because at time t=1s, the particle P is situated at equilibrium position and therefore the displacement should be zero at t=1.

Q3: iron but not copper should be used as metal core for transformer because iron is ferromagnetic material that can be magnetized to produce magetic field and induce e.m.f while copper cannot be magnetized.By Ns/Np=Vs/Vp, we can know that more no. of secondary coil and less no. of primary coil can result in the larger voltage reading.

Q3: you cannot use P=V^2/R to find the power loss because the electromotive force is also applied to the device, not the wire only, which has much lower voltage compared to the voltage of the device. However, as the wire and the device are connected in series, the current flowing across them is the same and hence you can use P=I^2xR to find out the power loss in heat.