Question

Given: F = mg where g = 9,8 N/kg (55 marks] 1. An experiment was done to see how the contact surface area affects the force of friction between a wooden block and a granite table. The contact surface area was changed by placing the block on its different sides. The force required to pull the block along at constant speed was measured with the spring-balance. Spring Scale 5cm m = 408 g 10cm 30cm 1.1 State a suitable hypothesis for this investigation. (2) 1.2 State the independent variable: (1) 1.3 State the dependent variable: (1) 1.4 State two important control (fixed) variables: (2) 1.5 is the force of KINETIC or STATIC friction being measured here? (1) 1.6 Suppose the spring-balance reads 2 N when the 408 g block is moving along the horizontal surface at constant speed. Draw a force diagram showing ALL the forces acting on the block. Label each force clearly as "Force of - on -- Give the size of each force in N. (14) Joe and Jabu obtained the following results: Force measured when on the 30 cm x 10 cm side: 2,1 N and 1,9 N Force measured when on the 30 cm x 5 cm side: 1,8 N and 2,2 N Force measured when on the 5 cm x 10 cm side: 2,0 N and 2,0 N

Answer 1

I Hypothesis The force of friction does not depend upon the contact area of the block all the lable 1.2 The undependent variable is the surface area of the block 1.3 The dependent variable as the reading of be spening balance in Eve pulling force of in the black ning lhe same block and tables surfaces CD Samel colond flow in lue room As the block uls moving at a constant speed , Kinetic friction is ANUARY 2012 being measured There 0 0 are using YAOVU 15 M T W T F 55 0 31 2 3 4 5 6 7 8 10 11 12 3 14 15 17 18 19 20 21 22

N = 3-9984 N FUN nq = 20 0.08 x 9.8 N 3-99 84 N table l tion force on the block surface by x. 9984 N a Cefficient of kinetic friction. Here the block is moving at constant o fext = fp = 20 i ll x 3.9984 - 2 a ll 0.5 Joel and Tabu look repeated measurements to get rid of experimental error Bauary KIS M T W T F S 6 7 8 9 10 11 12

Force on trial force on Ievala Aream) 0-3x0.1 20-03m? 1.9 0.3x0.05 -0.015 2.2 0.05 x 0, -0.005 20 2-0 Area 0.005 Vo.ols 0.03m? 1.10 Conclusion & Frictional force does not depend upon the the Surface area of the block. JANUARY 2012