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# physics midterm sample answer - 1 Student No Last Name...

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1 Student No. ________________ Last Name_____________ First Name _________________ The University of British Columbia - Coordinated Science Program Physics 101, Section 104 – Sample Midterm You re permitted to bring one 8.5 x 11 paper sheet with formulae and notes to the exam. Do all three questions. There are three pages to this test. Write your name on all three pages. Each problem is worth 10 points. Please use a simple non-programmable calculator. 1 atm = 1.013x10 5 N/m 2 ; air density = 1.28 kg/m 3 ; water density = 1000 kg/m 3 ; helium density = 0.179 kg/m 3 ; copper density = 8920 kg/m 3 ; steel density = 7870 kg/m 3 ; g = 9.81m/s 2 , Volume of sphere = 4/3 π r 3 Problem #1: (a) (5 marks) A beaker of water rests on an electronic balance that reads 996.0 g (9.77N) when the beaker contains only water. After this, a 2.60 cm diameter solid copper ball attached to a very light string is submerged in the water, but does not touch the bottom. i) (1) What would be the weight (in N) of the copper ball in air? ii) (2) What is the tension in the string when the ball is submerged in water? iii) (2) What is the new balance reading when the ball is submerged in water? i) Weight of ball = mg = ρ copper V copper g where V copper = 4/3 π (0.013m) 3 = 9.303 x 10 -6 m 3 weight = (8920 kg/m 3 )( 9.303 x 10 -6 m 3 )(9.81m/s 2 ) = 0.805N ii) the Buoyant force is ρ water V copper g = (1000kg/m 3 )( 9.303 x 10 -6 m 3 )(9.81m/s 2 ) = 0.0903 N Then the tension in the string is weight copper - Buoyant force = 0.805N – 0.0903N = 0.715011N

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physics midterm sample answer - 1 Student No Last Name...

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