Exploring Accumulations of Change

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AP Calculus BC › Exploring Accumulations of Change

Questions 1 - 10
1

A runner’s speed is $v(t)=2+\cos t$ m/s for $0\le t\le2\pi$; what distance is traveled?

$6\pi$ meters

$2\pi$ meters

$0$ meters

$2$ meters

$4\pi$ meters

Explanation

This problem assesses the skill of exploring accumulations of change by calculating the total distance traveled from a speed function. The speed is $v(t) = 2 + \cos t$ meters per second over $0$ to $2\pi$ seconds. Since speed is always positive, the distance is the integral of $v(t)$ from $0$ to $2\pi$, accumulating the rate of distance over time. This gives $[2t + \sin t]$ from $0$ to $2\pi$ = $4\pi + 0 = 4\pi$ meters. A tempting distractor is $2\pi$ meters, from integrating only the constant 2 and ignoring $\cos t$, but the full function must be included. In general, to find the net accumulation of a quantity from its rate of change, compute the definite integral of the rate function over the specified interval.

2

A leak changes oil amount at rate $A'(t)=-5\sqrt{t}$ liters/hour for $0\le t\le 4$; what is net change in oil?

$\frac{40}{3}$ liters

$\frac{80}{3}$ liters

$-20$ liters/hour

$-40$ liters

$-\frac{80}{3}$ liters

Explanation

This problem uses accumulation reasoning to find net change in oil from the leak rate. The net change equals ∫A'(t)dt = ∫(-5√t)dt from t = 0 to t = 4. Computing: ∫(-5t^(1/2))dt = -5(2t^(3/2)/3) = -10t^(3/2)/3 evaluated from 0 to 4 gives -10(8)/3 - 0 = -80/3 liters. Choice C incorrectly gives a rate (liters/hour) rather than the accumulated volume change. When integrating power functions with fractional exponents, apply the power rule carefully and track negative signs.

3

For $0\le t\le 3$, a population changes at rate $P'(t)=2e^{-t}$ thousand/day; what is total population increase?

$2(1-e^{-3})$ thousand

$6e^{-3}$ thousand/day

$2e^{-3}$ thousand

$6$ thousand

$2(1+e^{-3})$ thousand

Explanation

This problem requires accumulation reasoning to find total population increase from the rate of change. The total increase equals ∫P'(t)dt = ∫2e^(-t)dt from t = 0 to t = 3. Computing the integral: ∫2e^(-t)dt = -2e^(-t) evaluated from 0 to 3 gives -2e^(-3) - $(-2e^0$) = -2e^(-3) + 2 = 2(1 - e^(-3)) thousand. Choice C incorrectly gives a rate (thousand/day) rather than the accumulated population change. To find total change from an exponential rate, integrate carefully and evaluate at the bounds.

4

For $2 \le t \le 5$, temperature changes at rate $T'(t) = \frac{1}{t} - 2$ °C/min; what is net temperature change?

$-6$ °C/min

$\ln!\left(\frac{5}{2}\right) - 6$ °C

$6 - \ln!\left(\frac{5}{2}\right)$ °C

$\ln!\left(\frac{5}{2}\right) + 6$ °C

$\ln!\left(\frac{5}{2}\right)$ °C/min

Explanation

This problem requires accumulation reasoning to find net temperature change from the rate. The net change equals $\int T'(t) , dt = \int \left( \frac{1}{t} - 2 \right) dt$ from t = 2 to t = 5. Computing: $\int \left( \frac{1}{t} - 2 \right) dt = \ln |t| - 2t$ evaluated from 2 to 5 gives $(\ln 5 - 10) - (\ln 2 - 4) = \ln 5 - \ln 2 - 6 = \ln\left( \frac{5}{2} \right) - 6$ °C. Choice C incorrectly gives units of rate (°C/min) rather than accumulated temperature change. To find net change, integrate each term separately and combine the results at the bounds.

5

Water flows with rate $r(t)=\frac{6}{t+1}$ L/min for $0\le t\le3$; how many liters enter total?

$18\ln 4$

$\frac{18}{4}$

$6\ln 4$

$\frac{6}{4}$

$\ln 4$

Explanation

This problem tests the skill of exploring accumulations of change by using integration to find the total water volume from a flow rate. The total liters entering is the definite integral of r(t) = 6/(t+1) from t=0 to t=3, accumulating the flow over the interval. The antiderivative 6 ln|t+1| evaluated gives 6(ln4 - ln1) = 6 ln4 liters. This reflects the decreasing flow rate still yielding a positive accumulation. A tempting distractor like ln4 might arise from omitting the coefficient 6, but it fails as the integral requires multiplying by that factor. In general, to find the net accumulation over an interval, compute the definite integral of the rate function from the lower to upper limit.

6

The rate of change of profit is $R'(t)=t^2-4t$ thousand dollars/month for $0 \le t \le 4$; find net change in profit.

$-8$

$\frac{32}{3}$

$-\frac{32}{3}$

$8$

$0$

Explanation

This problem tests the skill of exploring accumulations of change by using integration to find the net change in profit from a rate of change. The net change is the definite integral of $R'(t) = t^2 - 4t$ from t=0 to t=4, accumulating the monthly profit variations. The antiderivative $\frac{1}{3}t^3 - 2t^2$ evaluated gives $\left( \frac{64}{3} - 32 \right) - 0 = -\frac{32}{3}$ thousand dollars. This negative accumulation results from the rate being negative initially and not fully compensated later. A tempting distractor like 0 might stem from finding where the rate is zero instead of integrating, but it fails as the integral captures the overall deficit. In general, to find the net accumulation over an interval, compute the definite integral of the rate function from the lower to upper limit.

7

A runner’s velocity is $v(t)=\sin t$ m/s for $0\le t\le\pi$; what is total distance traveled?​​

$\pi$ meters

$1$ meter

$-2$ meters

$0$ meters

$2$ meters

Explanation

This problem asks for total distance, not displacement, which requires accumulation reasoning with absolute values. Since v(t) = sin(t) ≥ 0 for 0≤t≤π, the runner always moves forward, so distance = ∫₀ᵖ|sin(t)|dt = ∫₀ᵖsin(t)dt = [-cos(t)]₀ᵖ = -cos(π)-(-cos(0)) = -(-1)-(-1) = 2 meters. Choice A (0 meters) would be the displacement if velocity changed sign symmetrically, but sin(t) stays positive on [0,π]. For distance traveled, integrate the absolute value of velocity; for displacement, integrate velocity directly.

8

For $0\le t\le6$, a machine’s production rate is $p(t)=\begin{cases}2t,&0\le t\le3\\12-2t,&3\le t\le6\end{cases}$; how many items are produced?

$18$ items

$36$ items

$12$ items

$9$ items

$6$ items

Explanation

This problem evaluates the skill of exploring accumulations of change by determining total production from a piecewise rate function. The production rate is 2t for 0 to 3 and 12 - 2t for 3 to 6. Total items produced is the integral over each piece, accumulating the rate over time. This gives [t²] from 0 to 3 = 9, plus [12t - t²] from 3 to 6 = 36 - 27 = 9, totaling 18 items. A tempting distractor is 36 items, from doubling the first integral without computing the second properly, but both pieces must be integrated separately. In general, to find the net accumulation of a quantity from its rate of change, compute the definite integral of the rate function over the specified interval.

9

A battery’s charge changes at $Q'(t)=-\frac{3}{t+1}$ coulombs/min for $0\le t\le3$; what is $Q(3)-Q(0)$?

$3\ln 4$ coulombs

$-3\ln 4$ coulombs

$-\dfrac{9}{4}$ coulombs

$-9$ coulombs

$\ln 4$ coulombs

Explanation

This problem assesses the skill of exploring accumulations of change by finding the net change in charge from a rate function. The rate is Q'(t) = -3/(t+1) coulombs per minute over 0 to 3 minutes. The net change Q(3) - Q(0) is the integral of Q'(t) from 0 to 3, accumulating the rate over time. This gives -3 [ln(t+1)] from 0 to 3 = -3(ln4 - ln1) = -3 ln4 coulombs. A tempting distractor is 3 ln4, from omitting the negative sign in the rate, but the sign indicates discharge. In general, to find the net accumulation of a quantity from its rate of change, compute the definite integral of the rate function over the specified interval.

10

A function satisfies $f'(x)=\frac{x}{1+x^2}$ for $0\le x\le2$; what is $f(2)-f(0)$?

$\ln 2$

$2$

$\dfrac{1}{2}\ln 5$

$\dfrac{2}{5}$

$\ln 5$

Explanation

This problem assesses the skill of exploring accumulations of change by finding the net change in a function from its derivative. The derivative is $f'(x) = \frac{x}{1 + x^2}$ over 0 to 2. The change $f(2) - f(0)$ is the integral of $f'(x)$ from 0 to 2, accumulating the rate over the interval. Using substitution $u = 1 + x^2$, this yields $\frac{1}{2} [\ln u]$ from 1 to 5 = $\frac{1}{2} \ln 5$. A tempting distractor is $\ln 5$, from forgetting the 1/2 factor in the substitution, but the $du = 2x , dx$ requires it. In general, to find the net accumulation of a quantity from its rate of change, compute the definite integral of the rate function over the specified interval.

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