A small block of mass 200 g starts at rest at A, slides to B where its speed is vB=8.0m/s,vB=8.0m/s, then slides along the horizontal surface a distance 10 m before coming to rest at C. (See below.) (a) What is the work of friction along the curved surface? (b) What is the coefficient of kinetic friction along the horizontal surface?

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Answer

given,

mass of the block = 200 g = 0.2 Kg

Velocity at A = 0 m/s

Velocity at B = 8 m/s

slide to the horizontal distance = 10 m

height of the block be = 4 m

potential energy of the block

    P = m g h

    P = 0.2 x 9.8 x 4

    P =7.84 J

kinetic energy

    [tex]KE = \dfrac{1}{2}mv^2[/tex]

    [tex]KE = \dfrac{1}{2}\times 0.2 \times 7.84^2[/tex]

    [tex]KE =6.14 J[/tex]

Work = P - KE

work = 7.84 - 6.14

work = 1.7 J

b) v² = u² + 2 a s

   0 = 8² - 2 x a x 10

   a = 3.2 m/s²

ma - μ mg = 0

 [tex]\mu = \dfrac{a}{g}[/tex]

 [tex]\mu = \dfrac{3.2}{9.8}[/tex]

 [tex]\mu = 0.327[/tex]

The work done by friction along the horizontal surface is 6.4 J, and the coefficient of kinetic friction along the horizontal surface is 0.327.

  • The given parameters;
  • mass of the rock, m = 200 g = 0.2 kg
  • final speed of the block, v = 8 m/s
  • distance traveled, s = 10 m

The normal force on the block is calculated as;

[tex]F_n = mg[/tex]

[tex]F_n = 0.2 \times 9.8\\\\F_n = 1.96 \ N[/tex]

The acceleration of the block over the given distance is calculated as;

[tex]v^2 = u^2 + 2as\\\\v^2 = 0 + 2as\\\\v^2 = 2as\\\\a = \frac{v^2}{2s} \\\\a = \frac{(8)^2}{2\times 10} \\\\a = 3.2 \ m/s^2[/tex]

The coefficient of kinetic friction is calculated as;

a = μg

[tex]\mu_k = \frac{a}{g} \\\\\mu_k =\frac{3.2}{9.8} \\\\\mu_k = 0.327[/tex]

The frictional force along the surface is calculated as;

[tex]F_k = \mu_k F_n\\\\F_k = 0.327\times 1.96\\\\F_k = 0.64 \ N[/tex]

The work done by friction along the horizontal surface is calculated as;

[tex]Work-done = F_k \times d\\\\Work-done = 0.64 \times 10\\\\Work-done = 6.4 \ J[/tex]

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