Page 128 Practice Problem 5.6: At what angle does the hill slope if the acceleration is g/2? Answer: 30°.

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**Example 5.6: Acceleration Down a Hill**

Now we’re ready to tackle the problem of an object sliding down a frictionless inclined plane. Suppose a child’s toboggan with negligible weight slides down a frictionless hill inclined at an angle α. The toboggan starts from rest. Find the acceleration of the toboggan. Let’s call the direction up the hill the positive x-axis and perpendicular to the hill's surface the positive y-axis.

**SET UP**

Figure 5.8 is our sketch for this problem. The only force acting on the toboggan is gravity (the weight, **w**). The component of the weight parallel to the hill causes the toboggan to accelerate. The perpendicular component of weight is balanced by the normal force.

**SOLUTION**

There is only one x-component of force, so

\[ \sum F_x = w \sin \alpha = ma_x \]

and since \( w = mg \), the acceleration is

\[ a_x = g \sin \alpha \]

The component equation \(\sum F_y = 0\) gives \( N - w \cos \alpha = 0 \). We see that the component of acceleration is zero because there is no net y-force.

**REFLECT**

The situations for different angles appear in this expression of \( a_x = g \sin \alpha \). When \( \alpha = 0 \), the acceleration is zero, as we should expect. This means any toboggan “sliding” down a hill will have no y-component of acceleration. When N equals w, the toboggan is stationary. A steep hill (α = 90°) leads to maximum acceleration: \( a_x = g \).

**Figure 5.8**

(a) The situation described.

(b) A free-body diagram shows the forces: **w** is decomposed into two components, one parallel \( (w \sin \alpha) \), and one perpendicular \( (w \cos \alpha) \). 

**Practice Problem**

What angle does the hill slope if the acceleration is 9/2? Answer: 30°.
Transcribed Image Text:**Example 5.6: Acceleration Down a Hill** Now we’re ready to tackle the problem of an object sliding down a frictionless inclined plane. Suppose a child’s toboggan with negligible weight slides down a frictionless hill inclined at an angle α. The toboggan starts from rest. Find the acceleration of the toboggan. Let’s call the direction up the hill the positive x-axis and perpendicular to the hill's surface the positive y-axis. **SET UP** Figure 5.8 is our sketch for this problem. The only force acting on the toboggan is gravity (the weight, **w**). The component of the weight parallel to the hill causes the toboggan to accelerate. The perpendicular component of weight is balanced by the normal force. **SOLUTION** There is only one x-component of force, so \[ \sum F_x = w \sin \alpha = ma_x \] and since \( w = mg \), the acceleration is \[ a_x = g \sin \alpha \] The component equation \(\sum F_y = 0\) gives \( N - w \cos \alpha = 0 \). We see that the component of acceleration is zero because there is no net y-force. **REFLECT** The situations for different angles appear in this expression of \( a_x = g \sin \alpha \). When \( \alpha = 0 \), the acceleration is zero, as we should expect. This means any toboggan “sliding” down a hill will have no y-component of acceleration. When N equals w, the toboggan is stationary. A steep hill (α = 90°) leads to maximum acceleration: \( a_x = g \). **Figure 5.8** (a) The situation described. (b) A free-body diagram shows the forces: **w** is decomposed into two components, one parallel \( (w \sin \alpha) \), and one perpendicular \( (w \cos \alpha) \). **Practice Problem** What angle does the hill slope if the acceleration is 9/2? Answer: 30°.
**Page 128 Practice Problem 5.6:**

At what angle does the hill slope if the acceleration is \( g/2 \)? 

**Answer:** \( 30^\circ \)
Transcribed Image Text:**Page 128 Practice Problem 5.6:** At what angle does the hill slope if the acceleration is \( g/2 \)? **Answer:** \( 30^\circ \)
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