AP Calculus BC 1.9 Connecting Multiple Representations of Limits Exam Style Questions - FRQ
Question • (Hard)
A particle moves along the \( x \)-axis with acceleration \( a(t) = 12t^2 – 4 \) ft/sec² for \( t \geq 0 \). Initial velocity \( v(0) = 0 \), position \( x(1) = 3 \) feet.
(a) Find velocity \( v(t) \).
(b) Use the table to estimate \( \lim_{t \to 1} v(t) \). Explain if it matches \( v(1) \) from (a).
(c) Find position \( x(t) \).
\( t \) (sec) | 0.9 | 0.99 | 0.999 | 1.001 | 1.01 | 1.1 |
\( v(t) \) (ft/sec) | -1.956 | -1.9996 | -1.999996 | -2.000004 | -2.0004 | -2.044 |
▶️ Answer/Explanation
Solution
(a) \( v(t) = \int (12t^2 – 4) \, dt = 4t^3 – 4t + C \). Using \( v(0) = 0 \), \( C = 0 \). \( \boxed{v(t) = 4t^3 – 4t} \).
(b) From table, as \( t \to 1^- \): \( v(0.999) = -1.999996 \to -2 \). As \( t \to 1^+ \): \( v(1.001) = -2.000004 \to -2 \). \( \boxed{\lim_{t \to 1} v(t) = -2} \). Compute \( v(1) = 4(1)^3 – 4(1) = 0 \), which differs from -2, indicating a removable discontinuity.
(c) \( x(t) = \int (4t^3 – 4t) \, dt = t^4 – 2t^2 + C \). With \( x(1) = 3 \), \( 1 – 2 + C = 3 \implies C = 4 \). \( \boxed{x(t) = t^4 – 2t^2 + 4} \).