In a laboratory investigation

PHYSICS · Multi-part · CBSE · Physics · Laws of Motion · Laws of Motion

Problem

In a laboratory investigation, a student measures the limiting friction

F_{\text{lim}}

acting on a wooden block sliding over a horizontal rough surface for different total masses placed on the block. The data obtained are: (a) Total mass on surface (kg): 1.0, 1.5, 2.0, 2.5, 3.0 (b) Measured

F_{\text{lim}}

(N): 4.2, 6.1, 8.0, 10.2, 12.0 (c) (i) Tabulate the corresponding normal reaction

N

for each mass value. (d) (ii) Draw a graph of

F_{\text{lim}}

versus

N

and obtain the best straight line. From its slope determine (a) the coefficient of static friction

\mu_s

, and (b) the uncertainty in

\mu_s

if the maximum scatter of points about the straight line is

\pm0.3\,\text{N}

in force and

\pm0.05\,\text{kg}

in mass. (e) (iii) A second set of measurements made after applying lubricant to the surface gives a new limiting friction of

2.4\,\text{N}

when the total mass is

1.2\,\text{kg}

. Using your earlier graph, estimate the coefficient of kinetic friction

\mu_k

after lubrication. (f) (iv) An unknown metal block placed on the same surface begins to slide when pulled with a horizontal force of

7.5\,\text{N}

. Using the value of

\mu_s

obtained, determine the mass of the metal block.

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