A block of mass 2.30 kg slides down a slope at an angle of 33° to the horizontal, with a constant velocity of 1.0 m s–1. Calculate the coefficient of dynamic friction between the slope and the block and express your answer to two significant figures.
Question
A block of mass 2.30 kg slides down a slope at an angle of 33° to the horizontal, with a constant velocity of 1.0 m s–1. Calculate the coefficient of dynamic friction between the slope and the block and express your answer to two significant figures.
Solution 1
To solve this problem, we need to use the principles of physics, specifically Newton's second law and the equations for friction. Here are the steps:
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Identify the forces acting on the block. These are gravity, the normal force from the slope, and friction.
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Resolve the gravitational force into components parallel and perpendicular to the slope. The component of gravity acting down the slope is given by mgsin(θ), where m is the mass of the block, g is the acceleration due to gravity (9.8 m/s²), and θ is the angle of the slope. The component of gravity acting perpendicular to the slope is mgcos(θ).
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The normal force is equal to the component of gravity acting perpendicular to the slope, so N = mg*cos(θ).
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The frictional force is given by f = μN, where μ is the coefficient of friction we're trying to find. Since the block is moving at a constant velocity, the frictional force must be equal to the component of gravity acting down the slope, so we have f = mg*sin(θ).
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Set these two expressions for the frictional force equal to each other and solve for μ:
μN = mg*sin(θ)
μmgcos(θ) = mgsin(θ)
μ = tan(θ)
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Substitute the given angle into this equation to find μ. Remember to convert the angle to radians first if your calculator is set to radian mode:
μ = tan(33°) = 0.65
So, the coefficient of dynamic friction between the slope and the block is 0.65 to two significant figures.
Solution 2
To solve this problem, we need to understand that the block is moving at a constant velocity. This means that the forces acting on the block are balanced.
Step 1: Identify the forces acting on the block There are three forces acting on the block:
- The weight of the block (W), which acts vertically downwards. This can be calculated using the formula W = mg, where m is the mass of the block and g is the acceleration due to gravity.
- The normal force (N), which acts perpendicular to the slope.
- The frictional force (F), which acts parallel to the slope and opposes the motion of the block.
Step 2: Resolve the weight into components The weight of the block can be resolved into two components: one acting perpendicular to the slope (Wcosθ) and one acting parallel to the slope (Wsinθ).
Step 3: Set up the equations of motion Since the block is moving at a constant velocity, the net force acting on it is zero. This gives us two equations:
- In the direction perpendicular to the slope: N = Wcosθ
- In the direction parallel to the slope: F = Wsinθ
Step 4: Calculate the frictional force The frictional force can be calculated using the equation F = μN, where μ is the coefficient of friction. Substituting the equation for N from step 3 gives F = μWcosθ.
Step 5: Equate the two expressions for the frictional force Setting the two expressions for the frictional force equal to each other gives μWcosθ = Wsinθ.
Step 6: Solve for the coefficient of friction Solving the equation from step 5 for μ gives μ = sinθ/cosθ = tanθ.
Substituting the given angle of 33° into this equation gives μ = tan(33°) = 0.65 to two significant figures.
Solution 3
To solve this problem, we need to use the equations of motion and the definition of the coefficient of friction. Here are the steps:
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First, we need to calculate the force of gravity acting on the block. This is given by F = mg, where m is the mass of the block and g is the acceleration due to gravity. So, F = 2.30 kg * 9.8 m/s^2 = 22.54 N.
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The force of gravity can be split into two components: one acting perpendicular to the slope (F_perpendicular = F * cos(33°)) and one acting parallel to the slope (F_parallel = F * sin(33°)).
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The force acting perpendicular to the slope is F_perpendicular = 22.54 N * cos(33°) = 18.91 N.
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The force acting parallel to the slope is F_parallel = 22.54 N * sin(33°) = 12.32 N.
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Since the block is moving at a constant velocity, the net force acting on it is zero. This means the force of friction acting on the block (F_friction) must be equal to the force acting parallel to the slope (F_parallel). So, F_friction = 12.32 N.
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The force of friction is also given by F_friction = μN, where μ is the coefficient of friction and N is the normal force. The normal force is equal to the force acting perpendicular to the slope (F_perpendicular). So, μ = F_friction / N = 12.32 N / 18.91 N = 0.65.
So, the coefficient of dynamic friction between the slope and the block is 0.65 to two significant figures.
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