Question

How do mass and speed affect the kinetic energy of an object?
Check all that are true.

When an object’s mass decreases, its kinetic energy increases.

When an object’s speed increases, its kinetic energy decreases.

When an object’s speed decreases, its kinetic energy decreases.

When an object’s mass increases, its kinetic energy increases.

Answer 1

The kinetic energy (KE) of an object is defined by the formula:

\[ KE = \frac{1}{2}mv^2 \]

where:
- \( m \) is the mass of the object,
- \( v \) is the speed (velocity) of the object.

Based on this formula, let's evaluate each statement:

1. **When an object’s mass decreases, its kinetic energy increases.**
**False.** If mass decreases and speed remains constant, the kinetic energy will decrease.

2. **When an object’s speed increases, its kinetic energy decreases.**
**False.** If speed increases while mass remains constant, the kinetic energy increases, because kinetic energy is proportional to the square of speed.

3. **When an object’s speed decreases, its kinetic energy decreases.**
**True.** If speed decreases while mass remains constant, the kinetic energy decreases, since it's proportional to the square of speed.

4. **When an object’s mass increases, its kinetic energy increases.**
**True.** If mass increases while speed remains constant, the kinetic energy increases, since kinetic energy is directly proportional to mass.

In summary, the true statements are:

- When an object’s speed decreases, its kinetic energy decreases.
- When an object’s mass increases, its kinetic energy increases.