Math Problem Statement

Two blocks with mass m1 = 7.5 kg and m2 = 24.5 kg are connected by a massless string over a frictionless and massless pulley. The angle of incline is equal to 52.5 degrees. The kinetic coefficient of friction between m1 and the incline is 0.24. What is the magnitude of acceleration of the system if m1 is moving up the hill. Also find the magnitude of acceleration of the system if m1 is moving down the incline

Solution

Let's solve the problem step by step by analyzing the forces acting on the two blocks and applying Newton's second law of motion. We'll handle both scenarios: (1) m1m_1 moving up the incline, and (2) m1m_1 moving down the incline.

Known Data:

  • m1=7.5kgm_1 = 7.5 \, \text{kg}
  • m2=24.5kgm_2 = 24.5 \, \text{kg}
  • Angle of incline, θ=52.5\theta = 52.5^\circ
  • Coefficient of kinetic friction, μk=0.24\mu_k = 0.24
  • Gravitational acceleration, g=9.8m/s2g = 9.8 \, \text{m/s}^2

Forces on m1m_1 (on the incline):

  • Gravitational force component along the incline: Fg1=m1gsinθF_{g_1} = m_1 g \sin\theta
  • Normal force: N1=m1gcosθN_1 = m_1 g \cos\theta
  • Frictional force: Ffriction=μkN1=μkm1gcosθF_{\text{friction}} = \mu_k N_1 = \mu_k m_1 g \cos\theta
  • Tension in the string: TT

Forces on m2m_2 (hanging vertically):

  • Gravitational force: Fg2=m2gF_{g_2} = m_2 g
  • Tension in the string: TT

Scenario 1: m1m_1 Moving Up the Incline

In this case, the tension in the string must overcome both the component of m1m_1's weight along the incline and the frictional force.

Equations for m1m_1 (moving up):

TFfrictionm1gsinθ=m1aT - F_{\text{friction}} - m_1 g \sin\theta = m_1 a Substitute for the friction force and component of weight: Tμkm1gcosθm1gsinθ=m1aT - \mu_k m_1 g \cos\theta - m_1 g \sin\theta = m_1 a T(0.24)(7.5)(9.8)cos(52.5)(7.5)(9.8)sin(52.5)=7.5aT - (0.24)(7.5)(9.8)\cos(52.5^\circ) - (7.5)(9.8)\sin(52.5^\circ) = 7.5a

Equation for m2m_2:

Since m2m_2 is moving down: m2gT=m2am_2 g - T = m_2 a Substitute g=9.8m/s2g = 9.8 \, \text{m/s}^2: (24.5)(9.8)T=24.5a(24.5)(9.8) - T = 24.5a Solve for TT: T=240.124.5aT = 240.1 - 24.5a

Solving for aa:

Now, substitute the expression for TT into the equation for m1m_1:

240.124.5a(0.24)(7.5)(9.8)cos(52.5)(7.5)(9.8)sin(52.5)=7.5a240.1 - 24.5a - (0.24)(7.5)(9.8)\cos(52.5^\circ) - (7.5)(9.8)\sin(52.5^\circ) = 7.5a Simplify and solve for aa.

Scenario 2: m1m_1 Moving Down the Incline

In this case, the forces acting on m1m_1 are helping it move down, while friction and the tension in the string resist this motion.

Equations for m1m_1 (moving down):

m1gsinθFfrictionT=m1am_1 g \sin\theta - F_{\text{friction}} - T = m_1 a Substitute for friction and the component of weight: (7.5)(9.8)sin(52.5)(0.24)(7.5)(9.8)cos(52.5)T=7.5a(7.5)(9.8)\sin(52.5^\circ) - (0.24)(7.5)(9.8)\cos(52.5^\circ) - T = 7.5a

Equation for m2m_2:

Tm2g=m2aT - m_2 g = -m_2 a Substitute g=9.8m/s2g = 9.8 \, \text{m/s}^2: T(24.5)(9.8)=24.5aT - (24.5)(9.8) = -24.5a Solve for TT: T=240.124.5aT = 240.1 - 24.5a

Solving for aa:

Substitute TT into the equation for m1m_1 and solve for aa.

Let me calculate the two accelerations for both cases.The magnitude of the acceleration in each case is as follows:

  1. When m1m_1 is moving up the incline, the acceleration of the system is approximately 5.35m/s25.35 \, \text{m/s}^2.

  2. When m1m_1 is moving down the incline, the acceleration of the system is approximately 6.02m/s26.02 \, \text{m/s}^2 (in the downward direction).

Would you like further details or have any questions?

Here are 5 related questions to extend your understanding:

  1. How does the angle of incline affect the acceleration of the system?
  2. What would happen if there were no friction on the incline?
  3. How does increasing m2m_2 impact the acceleration of the system?
  4. What is the effect of reducing the coefficient of kinetic friction on the system's motion?
  5. How would the system behave if the masses of m1m_1 and m2m_2 were equal?

Tip: When dealing with inclines, always break forces into components along the incline (parallel) and perpendicular to it for easy analysis!

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Math Problem Analysis

Mathematical Concepts

Newton's Second Law
Forces on Inclined Planes
Kinetic Friction
Pulley Systems
Trigonometry

Formulas

Newton's Second Law: F = ma
Gravitational Force on Incline: Fg = m * g * sin(θ)
Normal Force: N = m * g * cos(θ)
Frictional Force: Ff = μ * N
Tension and Acceleration Equations: T = m2 * g - m2 * a and T = m1 * a + Ff + m1 * g * sin(θ)

Theorems

Newton's Laws of Motion
Trigonometric Components of Forces

Suitable Grade Level

University Level (First Year Physics)