Practice

F = ma Formula – Newton’s Second Law Practice

F = ma — Newton’s second law (net force)

Net force equals mass times acceleration: F = m a. Rearrange to m = F/a or a = F/m. Weight is mg — different from the net force that produces a.

Guide — how to use this formula

1. 1. Convert mass to kilograms.
2. 2. Identify F_net, then F = ma (or rearrange).
3. 3. Don’t swap weight mg for net force unless the problem asks for weight.
4. 4. For multi-force problems, find F_net first.

Derivation

Newton’s second law relates the net external force on a body to its acceleration:

1. Definition (constant mass):
   F_{\mathrm{net}} = ma
2. With weight on Earth:
   W = mg

Always use the net force (sum of forces), not a single push if friction or weight also acts.

Examples

Example: 4 kg at 2 m/s²

F = 8 N.

Example: find a

F = 20 N, m = 5 kg → a = 4 m/s².

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