Math Problem Statement

The drawing shows three objects. They are connected by strings that pass over massless and friction-free pulleys. The objects move starting from rest, and the coefficient of kinetic friction between the middle object and the surface of the table is 0.122. (a) What is the acceleration of the three objects? (b) Find the tension in the string attached to the 25.0 kg object. (c) Find the tension in the string attached to the 10.0 kg object.

Solution

In this problem, we are dealing with three objects connected by strings over pulleys, with one object experiencing kinetic friction with the surface. Let's break it down step-by-step:

Step 1: Defining the forces

Let's assume the following:

  • Mass m1=10.0kgm_1 = 10.0 \, \text{kg} (the object on the left)
  • Mass m2=15.0kgm_2 = 15.0 \, \text{kg} (the middle object on the table)
  • Mass m3=25.0kgm_3 = 25.0 \, \text{kg} (the object on the right)
  • Coefficient of kinetic friction μk=0.122\mu_k = 0.122 (between m2m_2 and the surface)

Step 2: Free body diagrams

Forces on m1m_1 (10 kg object):

  • Gravitational force pulling it downward: Fg1=m1g=10.0kg×9.8m/s2=98NF_{g1} = m_1 g = 10.0 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 98 \, \text{N}.
  • Tension T1T_1 from the string acting upward.

The net force on m1m_1 is: F1=m1a=T1m1gF_1 = m_1 a = T_1 - m_1 g

Forces on m2m_2 (15 kg object on the table):

  • Tension T1T_1 on one side pulling to the left.
  • Tension T2T_2 on the other side pulling to the right.
  • Frictional force opposing the motion: Ff=μkm2g=0.122×15.0×9.8=17.91NF_f = \mu_k m_2 g = 0.122 \times 15.0 \times 9.8 = 17.91 \, \text{N}.

The net force on m2m_2 is: F2=m2a=T2T1FfF_2 = m_2 a = T_2 - T_1 - F_f

Forces on m3m_3 (25 kg object):

  • Gravitational force pulling it downward: Fg3=m3g=25.0kg×9.8m/s2=245NF_{g3} = m_3 g = 25.0 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 245 \, \text{N}.
  • Tension T2T_2 from the string acting upward.

The net force on m3m_3 is: F3=m3a=m3gT2F_3 = m_3 a = m_3 g - T_2

Step 3: Applying Newton's second law

From the equations above, we can solve for the acceleration aa and the tensions T1T_1 and T2T_2.

We have three equations:

  1. T1=m1gm1aT_1 = m_1 g - m_1 a
  2. T2T1Ff=m2aT_2 - T_1 - F_f = m_2 a
  3. m3gT2=m3am_3 g - T_2 = m_3 a

Substitute values and solve for aa, T1T_1, and T2T_2. I'll calculate the acceleration first.The acceleration of the three objects is approximately a=4.30m/s2a = 4.30 \, \text{m/s}^2.

Now, let's calculate the tensions T1T_1 and T2T_2.The tensions in the strings are as follows:

  • The tension T1T_1 in the string attached to the 10.0 kg object is approximately 54.98N54.98 \, \text{N}.
  • The tension T2T_2 in the string attached to the 25.0 kg object is approximately 137.45N137.45 \, \text{N}.

Would you like further details on any of the steps? Here are some related questions you could explore:

  1. How would the results change if the coefficient of kinetic friction was higher?
  2. What if the mass of the middle object increased? How would that affect the system's behavior?
  3. How does the tension in the strings relate to the objects' masses?
  4. What would happen if the pulleys were not frictionless?
  5. How does the direction of friction influence the forces on the middle object?

Tip: Always double-check your force equations when solving multi-object problems, as small sign errors can significantly impact the final results.

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Math Problem Analysis

Mathematical Concepts

Newton's Laws of Motion
Forces and Tension
Kinetic Friction
Systems of Equations

Formulas

Newton's Second Law: F = ma
Friction Force: F_f = μ_k * N
Gravitational Force: F_g = m * g

Theorems

Newton's Second Law of Motion

Suitable Grade Level

Grades 11-12