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Physics Paper 2, MAy/June. 2010  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments
Weakness/Remedies
Strength
Question 8

An X-ray tube operates at a potential of2500 V. lfthe power of the tube is 750 W, calculate the
speed of the electron striking the target.
[ e = 1.6 x 10-19 C; mass of electron = 9.1 x 10-31 kg]

Observation

Generally, candidates avoided this question, thus rendering it unpopular. Only few quoted the correct formula but substituted wrongly. Those that substitute correctly evaluated it wrongly. The expected answer is:
eV = 1/2mv2
1.6 x 10-19 x 2500 = Yz x 9.1 X 10-31 x v2
v2 = 8.79 X 1014
V = 2.96 X 107 ms2;

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