Power (College Board AP® Physics 1: Algebra-Based): Exam Questions

A carpenter pushes a box across a smooth wooden floor with her foot. She applies a force $F$ parallel to the displacement of the box, causing it to move at a constant speed $v$. The coefficient of kinetic friction between the box and the wooden floor is $\mu$.

Which of the following expressions describes the rate at which the carpenter does work on the box?

A Jack-in-a-box is composed of a toy mounted on a compressed spring that is released when the box is opened. The spring has a spring constant of $16\mathrm{N}/\mathrm{m}$ and is compressed $5.3\mathrm{cm}$ inside the box. The toy takes $0.08\mathrm{s}$ to spring out of the box.

Which of the following is most nearly the power delivered to the toy by the spring?

A warehouse worker pulls a crate of mass $18\mathrm{kg}$ along the floor with a coefficient of kinetic friction of $0.3$ using a rope applied at angle $24°$ from the horizontal. As the worker pulls the crate, the tension in the rope is $73\mathrm{N}$ and they move the crate a distance of $13\mathrm{m}$ in a time of $90\mathrm{s}$.

Which of the following is most nearly the average power delivered to the crate by the worker?

A constant force of $350\mathrm{N}$ is needed to move a sofa over a carpeted floor at a constant rate. The force is applied at an angle of $55°$ from the vertical.

If, at a given moment, the sofa is moving at a speed of $0.75\mathrm{m}/\mathrm{s}$, which of the following is most nearly the instantaneous power delivered to the sofa?

A car of mass $1000\mathrm{kg}$ accelerates up a slope inclined at $30.0°$. If the car moves at a constant speed of $10.0\mathrm{m}/\mathrm{s}$ while experiencing a resistive force of $500\mathrm{N}$, which of the following is the instantaneous power output of the engine?

An object of mass $200\mathrm{kg}$ floats in space. A force of $15\mathrm{N}$ is continuously applied to the object, causing it to accelerate at a constant rate. The object's initial velocity is measured from a nearby planet as having a magnitude of $30\mathrm{m}/\mathrm{s}$.

Which of the following is the instantaneous power applied to the object after 52 weeks?

A person pulls a crate along the floor with a rope. At time $t_1$, the person is applying a force to the rope at an angle of $15°$ to the floor.

Later, at time $t_2$, the person changes the angle of the rope while applying the same magnitude force. The speed of the crate at $t_2$ is a factor of 1.5 smaller than the speed at $t_1$ and the instantaneous power is a factor of 6 smaller.

Which of the following statements most nearly describes how the angle of the rope has changed?

A pendulum bob of mass $m$ swings from a light string of length $L$. When the bob is moving at a speed $v$, its angular displacement from the vertical is $\theta$. The string experiences tension force $T$ at this moment.

Which of the following shows the instantaneous power $P_{inst}$exerted by the tension force in the string and the weight of the bob?

Assume no air resistance.