Physics Challenge
Posted: Wed Mar 28, 2012 10:19 pm
This was a question in my Physics exam I had in January.
The movement of tennis balls can be tracked using a set of linked high-speed fixed-focus cameras placed around the court. The balls position is measured and its trajectory reconstructed. A tennis ball has a diamer of 67mm. When the ball is 10 metres from the camera, a sharp image of it is formed on a CCD 55mm behind the lens .
a)
i) Calculate the magnification of this image [1]
ii) Show that the power of the lens in the fixed focus camera is about 18D. [2]
iii) Show that the diameter of the image of the ball on the CCD is about 0.4mm. Make your method clear [2]
b) There are 70 pixels per mm on the CCD
i) Calculate the number of ipixels across the image of the 67mm diameter ball. [1]
ii) As the ball moves, its image moves across the CCD
Calculate the least distance the ball must move sideways for its image to move 1 pixel. [1]
c) The position of hte ball on 2 consecuative images can be used to determine the distance it has moved between images. Two such images give a value for the distance moved of 0.080m
State and explain the maximum possible value for this measurement based on your naswer to bii
Maximum Possible Value:
Explanation:
Good luck
I got 2/9 marks during the real exam on this question 
It should take you 9 minutes if you follow the examiners guidelines
The movement of tennis balls can be tracked using a set of linked high-speed fixed-focus cameras placed around the court. The balls position is measured and its trajectory reconstructed. A tennis ball has a diamer of 67mm. When the ball is 10 metres from the camera, a sharp image of it is formed on a CCD 55mm behind the lens .
a)
i) Calculate the magnification of this image [1]
ii) Show that the power of the lens in the fixed focus camera is about 18D. [2]
iii) Show that the diameter of the image of the ball on the CCD is about 0.4mm. Make your method clear [2]
b) There are 70 pixels per mm on the CCD
i) Calculate the number of ipixels across the image of the 67mm diameter ball. [1]
ii) As the ball moves, its image moves across the CCD
Calculate the least distance the ball must move sideways for its image to move 1 pixel. [1]
c) The position of hte ball on 2 consecuative images can be used to determine the distance it has moved between images. Two such images give a value for the distance moved of 0.080m
State and explain the maximum possible value for this measurement based on your naswer to bii
Maximum Possible Value:
Explanation:
Good luck
I got 2/9 marks during the real exam on this question It should take you 9 minutes if you follow the examiners guidelines