Math Problem Statement

(Figure 1) shows a block of mass m resting on a 20∘ slope. The block has coefficients of friction μs = 0.82 and μk = 0.51 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg.

A block of mass m rests on a 20-degree inclined plane with coefficients of friction μs = 0.82 and μk = 0.51. It is connected to a hanging block of mass 2.0 kg via a massless string over a massless, frictionless pulley.

Solution

To solve this problem, let's break it down step by step. We have two blocks, one on an inclined plane and another hanging over a pulley. The system involves friction on the slope and tension in the string. Here's how we can approach the problem:

Given:

  • Mass of the hanging block: m2=2kgm_2 = 2 \, \text{kg}
  • Mass of the block on the incline: m1=mkgm_1 = m \, \text{kg} (to be determined)
  • Angle of incline: θ=20\theta = 20^\circ
  • Coefficients of friction:
    • Static friction: μs=0.82\mu_s = 0.82
    • Kinetic friction: μk=0.51\mu_k = 0.51
  • Pulley: Massless and frictionless.

Step 1: Forces acting on block on incline (mass m1m_1):

  1. Gravitational force component parallel to the incline:
    Fgravity,=m1gsin(θ)F_{\text{gravity}, \parallel} = m_1 g \sin(\theta)
  2. Gravitational force component perpendicular to the incline:
    Fgravity,=m1gcos(θ)F_{\text{gravity}, \perp} = m_1 g \cos(\theta)
  3. Normal force:
    N=Fgravity,=m1gcos(θ)N = F_{\text{gravity}, \perp} = m_1 g \cos(\theta)
  4. Maximum static friction force:
    Ffriction=μsN=μsm1gcos(θ)F_{\text{friction}} = \mu_s N = \mu_s m_1 g \cos(\theta)

Step 2: Forces acting on hanging block (mass m2=2kgm_2 = 2 \, \text{kg}):

  • The gravitational force acting on the hanging block is Fgravity,m2=m2gF_{\text{gravity}, m_2} = m_2 g.

Step 3: Set up equations for equilibrium (no movement):

For the system to be in equilibrium, the net force acting on both masses must balance out.

  • For the hanging block (mass m2m_2):
    T=m2gT = m_2 g
    where TT is the tension in the string.

  • For the block on the incline (mass m1m_1):
    The tension in the string must balance the gravitational pull down the incline minus the frictional force:
    T=m1gsin(θ)FfrictionT = m_1 g \sin(\theta) - F_{\text{friction}}

So, combining these:

m2g=m1gsin(θ)μsm1gcos(θ)m_2 g = m_1 g \sin(\theta) - \mu_s m_1 g \cos(\theta)

Step 4: Solve for mass m1m_1:

Now, solve for m1m_1:

m2g=m1g(sin(θ)μscos(θ))m_2 g = m_1 g (\sin(\theta) - \mu_s \cos(\theta))

m1=m2sin(θ)μscos(θ)m_1 = \frac{m_2}{\sin(\theta) - \mu_s \cos(\theta)}

Substitute the known values:

  • m2=2kgm_2 = 2 \, \text{kg}
  • θ=20\theta = 20^\circ
  • μs=0.82\mu_s = 0.82
  • g=9.8m/s2g = 9.8 \, \text{m/s}^2

m1=2sin(20)0.82cos(20)m_1 = \frac{2}{\sin(20^\circ) - 0.82 \cos(20^\circ)}

Let's calculate that:

m1=20.34200.82×0.9397m_1 = \frac{2}{0.3420 - 0.82 \times 0.9397}

m1=20.34200.7705=20.4285m_1 = \frac{2}{0.3420 - 0.7705} = \frac{2}{-0.4285}

The negative value suggests that the block is moving. Thus, we need to switch to kinetic friction and solve using μk\mu_k.

Would you like me to continue with the kinetic friction case and solve for the motion of the system, or clarify anything so far?

Related Questions:

  1. What happens if the incline angle is increased?
  2. How does the solution change if the coefficient of kinetic friction is zero?
  3. What would happen if the mass of the hanging block is increased?
  4. How does the equilibrium change if the incline becomes frictionless?
  5. What role does the

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Math Problem Analysis

Mathematical Concepts

Newton's Laws of Motion
Friction
Equilibrium
Inclined Planes

Formulas

F_gravity_parallel = m1 * g * sin(θ)
F_gravity_perpendicular = m1 * g * cos(θ)
F_friction_max = μs * N
T = m2 * g
m1 = m2 / (sin(θ) - μs * cos(θ))

Theorems

Newton's Second Law of Motion
Laws of Friction

Suitable Grade Level

Grades 11-12