Question

(b) (i) state the equation linking moment, force and distance from the pivot.
(ii) calculate the moment of the 2 n weight.
state the unit.
moment = .........................unit = .........................

(4 marks)
(c) the student holds the ruler horizontal with the forcemeter at the 10 cm mark. he expects the reading on the forcemeter to be 12 n. the actual reading is 10 n.
explain why
(i) the correct reading should be larger than 12 n.
(ii) the actual reading is only 10 n.

Explanation:

Step1: State the moment - force - distance formula

The formula is $M = F\times d$, where $M$ is the moment, $F$ is the force and $d$ is the perpendicular distance from the pivot.

Step2: Calculate the moment of 2 N weight

Since no distance is given, assume a distance $d$ (if we assume a distance of 1 m for example). Then $M = 2\ N\times d$. If $d = 1\ m$, $M=2\ N\times1\ m = 2\ Nm$. The unit of moment is Newton - metre (Nm).

Step3: Analyze the force - meter reading in part (c)(i)

The student likely did not account for the weight of the ruler itself. The total upward force needed to balance the system (ruler and any other attached weights) is greater than just the force to balance the known weights. So the correct reading should be larger than 12 N as the weight of the ruler adds to the total downward - acting force that the force - meter must counteract.

Step4: Analyze the force - meter reading in part (c)(ii)

The actual reading is 10 N. This could be due to incorrect calibration of the force - meter, or some external factors like air resistance (although air resistance is usually negligible in such simple set - ups), or an error in the experimental set - up such as the ruler not being perfectly horizontal or the pivot not being frictionless.

Answer:

(b)(i) $M = F\times d$
(b)(ii) moment = 2 Nm (assuming $d = 1\ m$), unit = Nm
(c)(i) The weight of the ruler was not considered, increasing the total downward force.
(c)(ii) Possible reasons include force - meter calibration error, non - ideal experimental conditions like non - horizontal ruler or non - frictionless pivot.