Introducing Calculus
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AP Calculus BC › Introducing Calculus
A spring’s length is $L(t)=12-3e^{-0.5t}$ cm; interpret $L'(1)$.
The spring’s average length change from $t=0$ to $t=1$
The spring’s instantaneous rate of length change at $t=1$
The total length change from $t=0$ to $t=1$
The average rate of length change from $t=1$ to $t=2$
The spring’s length at $t=1$
Explanation
This problem tests the concept of instantaneous rate of change through derivatives. For a length function $L(t)$, the derivative $L'(t)$ represents the instantaneous rate at which length is changing at time $t$. Unlike average rate of change, which would be computed as $\frac{L(1)-L(0)}{1-0}$ over an interval, $L'(1)$ gives the exact rate of length change at the precise moment $t=1$. Choice A is tempting because it mentions rate, but it describes an average over an interval rather than the instantaneous rate at a point. When interpreting derivatives in physical contexts, remember that $f'(a)$ always represents how quickly the quantity is changing at the specific instant $t=a$.
A cyclist’s position is $x(t)=4t^2+2t$ meters; what does $x'(6)$ represent?
The cyclist’s average velocity from $t=0$ to $t=6$
The cyclist’s position at $t=6$
The cyclist’s average acceleration from $t=0$ to $t=6$
The cyclist’s instantaneous velocity at $t=6$
The cyclist’s displacement from $t=5$ to $t=6$
Explanation
This problem tests understanding of instantaneous rate of change through derivatives. For a position function $x(t)$, the derivative $x'(t)$ represents instantaneous velocity at time $t$. While average velocity would be calculated as $\frac{x(6)-x(0)}{6-0}$ over an interval, the instantaneous velocity $x'(6)$ gives the exact speed and direction at the specific moment $t=6$. Choice A fails because it describes average velocity over a time interval rather than instantaneous velocity at a point. When working with derivatives in kinematics, remember that $x'(a)$ always represents the instantaneous velocity (rate of change of position) at the precise time $t=a$.
A car’s speed is $v(t)=20+3t$ m/s; what does $v'(4)$ represent?
The car’s total distance traveled by $t=4$
The car’s average acceleration from $t=0$ to $t=4$
The car’s average velocity from $t=0$ to $t=4$
The car’s instantaneous acceleration at $t=4$
The car’s instantaneous velocity at $t=4$
Explanation
This problem tests understanding of instantaneous rate of change through derivatives. For a velocity function $v(t)$, the derivative $v'(t)$ represents instantaneous acceleration at time $t$. Unlike average acceleration, which would be $\frac{v(4)-v(0)}{4-0}$ over an interval, $v'(4)$ gives the exact acceleration at the specific moment $t=4$. Choice C fails because it describes instantaneous velocity, but we need the derivative of velocity, which is acceleration. When working with derivatives in kinematics, remember that if $v(t)$ is velocity, then $v'(a)$ always represents the instantaneous acceleration at the precise time $t=a$.
A freezer’s temperature is $T(t)=-5-2t+0.1t^2$ °C; what does $T'(9)$ represent?
The temperature at $t=9$
The average temperature change from $t=0$ to $t=9$
The average rate of temperature change from $t=9$ to $t=18$
The instantaneous rate of temperature change at $t=9$
The total temperature decrease from $t=0$ to $t=9$
Explanation
This question examines the concept of instantaneous rate of change via derivatives. For a temperature function $T(t)$, the derivative $T'(t)$ represents the instantaneous rate at which temperature is changing at time $t$. While average temperature change would be calculated as $\frac{T(9)-T(0)}{9-0}$ over an interval, the instantaneous rate $T'(9)$ tells us exactly how fast the temperature is changing at the precise moment $t=9$. Choice A is tempting because it mentions rate, but it describes an average over an interval rather than the instantaneous rate at a point. To identify instantaneous rates from derivatives, look for expressions like $f'(a)$ where the derivative is evaluated at a specific input value, indicating the instantaneous rate of change at that moment.
A camera’s battery charge is $Q(t)=100-3t-0.1t^2$ percent; interpret $Q'(8)$.
The total battery drained from $t=0$ to $t=8$
The battery charge at $t=8$
The average battery drain from $t=8$ to $t=16$
The average battery drain from $t=0$ to $t=8$
The instantaneous battery drain rate at $t=8$
Explanation
This question focuses on interpreting instantaneous rate of change from derivatives. For a charge function $Q(t)$, the derivative $Q'(t)$ represents the instantaneous rate at which battery charge is changing at time $t$. While average battery drain would be calculated as $\frac{Q(0)-Q(8)}{8-0}$ over an interval, the instantaneous drain rate $Q'(8)$ tells us exactly how fast the charge is decreasing at the precise moment $t=8$. Choice A is incorrect because it describes average battery drain over a time interval rather than instantaneous drain rate at a point. To recognize instantaneous rates in applied problems, look for derivatives evaluated at specific points, which always represent how quickly the quantity is changing at that exact moment.
A stone’s height is $y(t)=80-16t^2$ feet; what does $y'(1)$ represent?
The stone’s total distance fallen from $t=0$ to $t=1$
The stone’s height at $t=1$
The stone’s average acceleration from $t=0$ to $t=1$
The stone’s average velocity from $t=0$ to $t=1$
The stone’s instantaneous velocity at $t=1$
Explanation
This question focuses on interpreting instantaneous rate of change from derivatives. For a height function $y(t)$, the derivative $y'(t)$ represents instantaneous velocity at time $t$. While average velocity would be calculated as $\frac{y(1)-y(0)}{1-0}$ over an interval, the instantaneous velocity $y'(1)$ tells us exactly how fast the stone is moving vertically at the precise moment $t=1$. Choice A fails because it describes average velocity over a time interval rather than instantaneous velocity at a point. To recognize instantaneous rates in motion problems, look for derivatives evaluated at specific points, which always represent the instantaneous rate of change of position (velocity) at that exact moment.
A kite’s height is $h(t)=10t-0.5t^2$ meters; what does $h'(7)$ represent?
The kite’s instantaneous vertical speed at $t=7$
The kite’s height at $t=7$
The kite’s average vertical acceleration from $t=6$ to $t=7$
The kite’s average vertical speed from $t=0$ to $t=7$
The kite’s total change in height from $t=0$ to $t=7$
Explanation
This problem tests understanding of instantaneous rate of change through derivatives. For a height function $h(t)$, the derivative $h'(t)$ represents instantaneous vertical velocity at time $t$. Unlike average vertical speed, which would be $\frac{h(7)-h(0)}{7-0}$ over an interval, $h'(7)$ gives the exact speed and direction at the specific moment $t=7$. Choice A is tempting because it mentions speed, but it describes an average over an interval rather than the instantaneous speed at a point. When working with derivatives in motion problems, remember that $h'(a)$ always represents the instantaneous velocity (rate of change of position) at the precise time $t=a$.
A cup cools with $T(t)=20+60e^{-0.2t}$; what does $T'(10)$ represent?
The temperature at $t=10$
The average temperature from $t=0$ to $t=10$
The total temperature drop from $t=0$ to $t=10$
The average cooling rate from $t=0$ to $t=10$
The instantaneous cooling rate at $t=10$
Explanation
This question examines the concept of instantaneous rate of change via derivatives. For a temperature function $T(t)$, the derivative $T'(t)$ represents the instantaneous rate at which temperature is changing at time $t$. While average cooling rate would be calculated as $\frac{T(0)-T(10)}{10-0}$ over an interval, the instantaneous cooling rate $T'(10)$ tells us exactly how fast the temperature is changing at the precise moment $t=10$. Choice A is tempting because it mentions rate, but it describes an average over an interval rather than the instantaneous rate at a point. To identify instantaneous rates from derivatives, look for expressions where the derivative is evaluated at specific input values, representing how quickly the quantity changes at that exact moment.
The cost is $C(x)=500+20x+0.1x^2$ dollars; what does $C'(100)$ represent?
The profit when $x=100$
The average cost per item for producing 100 items
The average rate cost changes from $x=0$ to $x=100$
The total cost to produce 100 items
The instantaneous rate cost changes with production at $x=100$
Explanation
This question examines the concept of instantaneous rate of change via derivatives. For a cost function $C(x)$, the derivative $C'(x)$ represents the instantaneous rate at which cost changes with production level at $x$ units. While average cost per item would be $\frac{C(100)}{100}$ or average rate would be $\frac{C(100)-C(0)}{100-0}$, the instantaneous rate $C'(100)$ tells us exactly how fast cost is increasing with production at the specific level $x=100$. Choice A is incorrect because it describes average cost per item rather than the instantaneous rate of cost change. To identify instantaneous rates in economics, look for derivatives evaluated at specific input values, representing marginal rates of change.
A city’s population is $N(t)=1.2+0.05t^2$ million; interpret $N'(4)$.
The total population increase from $t=0$ to $t=4$
The average population change from $t=0$ to $t=4$
The instantaneous population growth rate at $t=4$
The average growth rate from $t=4$ to $t=8$
The population at $t=4$
Explanation
This problem tests understanding of instantaneous rate of change through derivatives. For a population function $N(t)$, the derivative $N'(t)$ represents the instantaneous growth rate at time $t$. Unlike average growth rate, which would be $\frac{N(4)-N(0)}{4-0}$ over an interval, $N'(4)$ gives the exact rate of population growth at the specific moment $t=4$. Choice A is incorrect because it describes average population change over a time interval rather than instantaneous growth rate at a point. When working with derivatives in population models, remember that $N'(a)$ always represents the instantaneous rate at which the population is growing at the precise time $t=a$.