WJEC Physics for AS Level: Revision Workbook

Q1 The candela (cd) is one of the seven SI base units. It is not used in A level physics. State the names and symbols of the other six SI base units. 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Q2 Newton’s second law of motion can be written F = ma . (a) State the SI unit of force and give its symbol. [1] ......................................................................................................................................................................................................................................................................................................................................... (b) Use the equation to write the unit of force in terms of the metre (m), kilogram (kg) and second (s). 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(c) Use the answer to (b) and the defining equation for work to show that the joule, J, can be expressed as kg m 2 s −2. 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Q3 Very slow-moving objects in air experience a drag force, F , proportional to their speed, v , through the air, that is F = kv , where k is a constant. (a) Show that the unit of k can be written [ k ] = kg s −1 . 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(b) For more rapidly moving objects, the drag equation becomes F = KAv 2 , where A is the cross-sectional area and K is a constant (different from that in part (a)). Express the unit of K in terms of the base SI units. 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Q4 The area, A , of a circle is related to its radius by the equation A = Ɏ” 2 . Explain why Ɏ has no unit. [1] ......................................................................................................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................................................................................................... 12 | WJEC Physics for AS Level: Revision Workbook | Unit 1: Motion, Energy and Matter