Home / IB Mathematics SL 2.5 Linear and other models AI HL Paper 1- Exam Style Questions

IB Mathematics SL 2.5 Linear and other models AI HL Paper 1- Exam Style Questions

IB Mathematics SL 2.5 Linear and other models AI HL Paper 1- Exam Style Questions- New Syllabus

Question

In a baseball game, Sakura is the batter standing beside home plate. The ball is thrown towards home plate along a path that can be modelled by the following function: \( y = -0.045x + 2 \), where \( x \) is the horizontal distance of the ball from the point the ball is thrown and \( y \) is the vertical height of the ball above the ground. Both measured in metres. The outcome of the throw is called a strike if the height of the ball is between 0.53 m and 1.24 m at some point while it travels over home plate. The length of home plate is 0.43 m.

a) When the ball reaches the front of home plate, the height of the ball above the ground is 1.25 m. The height of the ball changes by \( a \) metres as the ball travels over the length of home plate.

(i) Find the value of \( a \).

(ii) Justify why this throw is a strike.

b) On the next throw, Sakura hits the ball towards a wall that is 5 metres high. The horizontal distance of the wall from the point where the ball was hit is 96 metres. The path of the ball after it is hit can be modelled by the function \( h(d) = -0.01d^2 + 1.04d + 0.66 \), for \( h, d > 0 \). In this model, \( h \) is the height of the ball above the ground and \( d \) is the horizontal distance of the ball from the point where it was hit. Both \( h \) and \( d \) are measured in metres. Determine whether the ball will go over the wall. Justify your answer.

▶️ Answer/Explanation
Markscheme

(a) (i) METHOD 1
Attempt to find change in height of the ball using gradient (M1)
\( \frac{a}{0.43} = -0.045 \)
\( a = -0.045 \times 0.43 \)
\( a = -0.01935 \) (m) (\(-0.0194\) (m)) (A1)
Result: \( a = -0.0194 \) m [2]

METHOD 2
Attempt to find height at back of home plate (M1)
Horizontal distance to the front of home plate: \( y = 1.25 = -0.045x + 2 \implies -0.045x = -0.75 \implies x = \frac{0.75}{0.045} \approx 16.6667 \) m
Distance to back of home plate: \( 16.6667 + 0.43 = 17.0967 \) m
Height at back: \( y = -0.045 \times 17.0967 + 2 \approx -0.76935 + 2 = 1.23065 \) m
\( a = 1.23065 – 1.25 = -0.01935 \) (m) (\(-0.0194\) (m)) (A1)
Result: \( a = -0.0194 \) m [2]

(ii)
Height at back of home plate: \( 1.23065 \) m (from (i)) (M1)
Strike zone: \( 0.53 < 1.23065 < 1.24 \) (A1)
Therefore, the throw is a strike (R1)
Result: The throw is a strike because the height at the back of home plate (1.23065 m) is between 0.53 m and 1.24 m [2]

(b) METHOD 1
Indication of \( d = 96 \) in the function \( h(d) \) or its graph (M1)
\( h(96) = -0.01(96)^2 + 1.04 \cdot 96 + 0.66 \) (A1)
\( h(96) = -0.01 \cdot 9216 + 99.84 + 0.66 = -92.16 + 99.84 + 0.66 = 8.34 \) (m) (A1)
\( 8.34 > 5 \), so the ball will go over the wall (A1)
Result: The ball goes over the wall because its height at 96 m (8.34 m) exceeds the wall height (5 m) [2]

METHOD 2
Indication of \( h = 5 \) in the function \( h(d) \) or its graph (M1)
Solve: \( 5 = -0.01d^2 + 1.04d + 0.66 \) (A1)
\( -0.01d^2 + 1.04d + 0.66 – 5 = 0 \implies -0.01d^2 + 1.04d – 4.34 = 0 \)
\( d^2 – 104d + 434 = 0 \)
Discriminant: \( \Delta = (-104)^2 – 4 \cdot 1 \cdot 434 = 10816 – 1736 = 9080 \)
\( d = \frac{104 \pm \sqrt{9080}}{2} \approx \frac{104 \pm 95.26}{2} \)
\( d \approx 99.63 \) or \( d \approx 4.37 \) (m) (A1)
Since \( 96 < 99.63 \), the ball reaches 5 m after 96 m, so it is above 5 m at \( d = 96 \), thus it goes over the wall (A1)
Result: The ball goes over the wall because it is above 5 m at \( d = 96 \) m [2]

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