Physics 5054 · O Level · Motion

Motion — practice question

A student explores how parachute area changes the time it takes to descend. He trims a square from an A4 sheet of paper to form the parachute, then fastens it to an eraser with four equal-length pieces of thin string, as shown in Fig. 2.1. An A4 sheet of paper is the same size as one page of the examination paper. The student holds the top of the parachute against the ceiling. He lets it go and measures the time $t$ for the eraser to reach the floor.
(a(i))[2]

Calculate $t_{av}$, the mean value of $t$. Give your answer to 2 decimal places.

(a(ii))[1]

Suggest a reason why the value of $t_{av}$ is not stated to more than 2 decimal places.

(a(iii))[1]

Suggest a reason why the distance that the parachute falls is chosen to be as large as possible.

(a(iv))[1]

The length $l$ of one side of the parachute is $21.0\,\text{cm}$. Calculate the area $A$ of the paper used to make the parachute.

(a(v))[1]

Suggest a reason why the student cannot make a parachute with an area greater than your answer to (a)(iv) when using the sheet of A4 paper.

(b(i))[1]

On Fig. 2.2, write your values of $A$ and $t_{av}$ for $l = 21.0\,\text{cm}$.

(b(ii))[1]

On Fig. 2.2, complete the column for $A$.

(b(iii))[4]

On Fig. 2.3, plot the graph of $t_{av} \/ \text{s}$ on the $y$-axis against $A \/ \text{cm}^2$ on the $x$-axis. Start your axes from $(100, 0.7)$. Draw the straight line of best fit.

(b(iv))[1]

When extended, the line of best fit misses the origin $(0,0)$. Explain why.

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