Forces and Newton’s laws (AS Unit 2: Applied Mathematics A) — WJEC A-Level Mathematics
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Forces and Newton’s laws (AS Unit 2: Applied Mathematics A) explained
Weight is the downward gravitational force acting on a particle of mass m, given by W = mg, where g is the local gravitational acceleration.
Read the full explanation
Near the surface of the Earth, standard mechanics assumes g = 9.8 m s⁻² (or 9.81 m s⁻² or 10 m s⁻² depending on specification instructions). For a particle falling freely under gravity in a vacuum or where air resistance is negligible, the only force acting is weight, resulting in constant vertical acceleration a = g downward. Candidates establish a clear sign convention (e.g. upwards positive, so a = −g = −9.8 m s⁻²) when applying constant acceleration equations.
Your focus
- Calculate the weight of a particle from its mass using gravitational acceleration g = 9.8 m s⁻².
- Model vertical motion under gravity using consistent sign conventions and suvat formulas.
- Determine key vertical flight characteristics including time of flight and maximum height reached.
Forces and Newton’s laws (AS Unit 2: Applied Mathematics A) exam tips
Marking Points
- calculating weight using W = mg with the specified numerical value of g
- establishing a consistent vertical sign convention (e.g. upwards positive implies a = −9.8 m s⁻²)
- applying suvat equations to vertical motion under gravity to find maximum height or time of flight
Examiner Tips
- 💡Always use the value of g specified in the rubric (standard WJEC is g = 9.8 m s⁻² unless stated otherwise).
- 💡At the maximum height of vertical projection, the instantaneous vertical velocity is zero (v = 0).
Common Mistakes
- using g = 9.8 with inconsistent signs, such as taking initial velocity upwards as positive and acceleration as positive 9.8
- confusing mass in kg with weight in N, or treating g as a force rather than an acceleration