3 Work and Energy Free Online FlashCards

What is the SI unit of work and energy?

Work and energy are measured in joules; $1\,\text{J}=1\,\text{N}\cdot\text{m}$.

How do you calculate work by a constant force?

For a constant force, $W=F\,\Delta r\cos\theta$, where $\theta$ is the angle between force and displacement.

How does the force–displacement angle determine the sign of work?

Work is positive when force has a component along displacement, negative when it opposes displacement, and zero when it is perpendicular.

How is work calculated when force varies along a path?

For a varying force, $W=\int_A^B \vec F\cdot d\vec r$. In one dimension, $W=\int_{x_A}^{x_B}F_x(x)\,dx$.

What does the signed area under a force–position graph represent?

In one dimension, work is the signed area under the force-versus-position graph.

What is the formula for translational kinetic energy?

Translational kinetic energy is $K=\frac{1}{2}mv^2$, where $m$ is mass and $v$ is speed.

What does the work–energy theorem state?

The net work on an object equals its change in kinetic energy: $W_{\text{net}}=\Delta K=K_f-K_i$.

What defines a conservative force?

A conservative force does work between two positions that depends only on those positions, not on the path taken.

How is a conservative force’s work related to potential-energy change?

The change in potential energy is the negative of the work done by the conservative force: $\Delta U=-W_{\text{conservative}}$.

What is gravitational potential energy near Earth’s surface?

Near Earth’s surface, gravitational potential energy is $U_g=mgh$, relative to a chosen zero-height level.

What is the potential energy of an ideal stretched or compressed spring?

For an ideal spring displaced by $x$ from its relaxed length, $U_s=\frac{1}{2}kx^2$, where $k$ is the spring constant.

What is mechanical energy?

Mechanical energy is the sum of kinetic and potential energy: $E_{\text{mech}}=K+U$.