Math Problem Statement

A 2.0 kg block slides down a flat incline. At one instant, the block is 3.0 m above the bottom of the incline and has a speed of 1.0 m/s down the incline. If the incline is 5.0 m long, and the coefficient of kinetic friction between the block and the incline is μk = 0.75, what is the block’s speed when it reaches the bottom of the incline?

Solution

We are asked to find the block's speed when it reaches the bottom of the incline. Let's break this down step-by-step.

Given:

  • Mass of the block, m=2.0kgm = 2.0 \, \text{kg}
  • Initial speed, vi=1.0m/sv_i = 1.0 \, \text{m/s}
  • Height above the bottom, h=3.0mh = 3.0 \, \text{m}
  • Length of the incline, d=5.0md = 5.0 \, \text{m}
  • Coefficient of kinetic friction, μk=0.75\mu_k = 0.75
  • Acceleration due to gravity, g=9.8m/s2g = 9.8 \, \text{m/s}^2

Steps:

  1. Calculate the gravitational force component along the incline: The block is sliding down the incline due to gravity, which has a component along the incline.

    The angle of the incline θ\theta can be found using:

    \quad \Rightarrow \quad \theta = \sin^{-1}(0.6)$$ Now, the component of gravitational force along the incline: $$F_{\text{gravity}} = mg \sin \theta$$
  2. Frictional force: The frictional force opposing the motion is: Ffriction=μkmgcosθF_{\text{friction}} = \mu_k mg \cos \theta Here, cosθ=1sin2θ=10.62=0.8\cos \theta = \sqrt{1 - \sin^2 \theta} = \sqrt{1 - 0.6^2} = 0.8.

  3. Net force and acceleration: The net force along the incline is the difference between the gravitational force and the frictional force: Fnet=FgravityFfriction=mgsinθμkmgcosθF_{\text{net}} = F_{\text{gravity}} - F_{\text{friction}} = mg \sin \theta - \mu_k mg \cos \theta The net acceleration aa is: a=Fnetm=g(sinθμkcosθ)a = \frac{F_{\text{net}}}{m} = g (\sin \theta - \mu_k \cos \theta)

  4. Using kinematic equations: To find the final velocity vfv_f, we use the kinematic equation: vf2=vi2+2adv_f^2 = v_i^2 + 2ad Solving for vfv_f: vf=vi2+2adv_f = \sqrt{v_i^2 + 2ad}

Now, let’s calculate the individual components.

1. Calculate the angle θ\theta:

θ=sin1(0.6)=36.87\theta = \sin^{-1}(0.6) = 36.87^\circ

2. Gravitational and frictional forces:

Fgravity=2.0×9.8×sin(36.87)=11.76NF_{\text{gravity}} = 2.0 \times 9.8 \times \sin(36.87^\circ) = 11.76 \, \text{N} Ffriction=0.75×2.0×9.8×cos(36.87)=11.76NF_{\text{friction}} = 0.75 \times 2.0 \times 9.8 \times \cos(36.87^\circ) = 11.76 \, \text{N}

3. Net force and acceleration:

Fnet=11.7611.76=0NF_{\text{net}} = 11.76 - 11.76 = 0 \, \text{N} [ a = g (\sin \theta - \mu_k \cos \theta) =

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Math Problem Analysis

Mathematical Concepts

Kinematics
Work-Energy Theorem
Trigonometry
Frictional Force

Formulas

F_gravity = m * g * sin(θ)
F_friction = μ_k * m * g * cos(θ)
a = g(sin(θ) - μ_k * cos(θ))
v_f^2 = v_i^2 + 2 * a * d

Theorems

Kinetic Energy Theorem
Newton's Second Law of Motion

Suitable Grade Level

Grades 10-12