Fig. 1 shows a small steel ball falling through a transparent tube of oil in a laboratory investigation. A student marks two points 100 mm apart on the tube...
Question 1 Report
Fig. 1 shows a small steel ball falling through a transparent tube of oil in a laboratory investigation. A student marks two points 100 mm apart on the tube and uses light gates to measure the time taken by the ball between them. The ball has already travelled far enough to move at terminal velocity between the marks. The measured time is 0.80 s. The oil is at a constant temperature, so its viscosity does not change during this reading. The student repeats the experiment with a larger ball.
(a) Use the information to calculate the terminal velocity of the small ball in m/s. [2]
(b) Give the direction of the resistive force exerted by the oil on the falling ball. [1]
(c) Describe how the forces on the ball compare when it travels between the two marks. [2]
Answer Details
- (a) First convert the distance: \(100\text{ mm}=0.100\text{ m}\).
\[v=\frac{d}{t}=\frac{0.100\text{ m}}{0.80\text{ s}}=0.125\text{ m s}^{-1}\]
The terminal velocity is 0.125 m s−1. [2] - (b) The resistive force from the oil acts upwards, opposite to the falling motion. [1]
- (c) Weight acts downwards and the resistive force acts upwards. At terminal velocity they are equal in size, so the resultant force is zero. [2]
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