Physics 5054 · O Level · Forces

Forces — practice question

A student is examining the upward force acting on a cylinder in water. Before the cylinder is put into the water, he hangs it from the end of a newton meter, as illustrated in Fig. 3.1.
(a)[1]

State the cylinder’s weight before it is placed in the water.

(b(i))[1]

The student then lowers the cylinder into the beaker of water until it is completely submerged. The reading obtained is shown in Fig. 3.2. State the new reading shown in Fig. 3.2.

(b(ii))[1]

Calculate the upward force on the cylinder caused by the water.

(c(i))[1]

The cylinder has height $h=6.5\,\text{cm}$ and diameter $3.8\,\text{cm}$. Calculate the volume $V$ of the cylinder using $V = \frac{\pi d^{2}h}{4}$.

(c(ii))[1]

The diameter $d$ is measured using a ruler. Describe how this can be done accurately. You may include a diagram if you want.

(c(iii).1)[1]

The theory states that the upward force on the cylinder is: upward force $= V g \rho$, where $g = 10\,\text{N kg}^{-1}$ and $\rho = 0.0010\,\text{kg cm}^{-3}$. Use your value of $V$ from (c)(i) to calculate the upward force predicted by this theory.

(c(iii).2)[1]

State whether the value of the upward force found in (b)(ii) supports the theory. Give a reason for your answer.

Worked solution & mark scheme

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