The number one mistake people make on these problems is confusing mass and weight. Remember that mass is the amount of "stuff" in an object, which stays the same no matter where you move it. Weight measures the force of gravity on that "stuff," which changes if you move through space. Here's are a couple mnemonic to keep your units distinct:  Mass is in units of grams or kilograms. Both mass and gram contain an m. Weight is in units of newtons. Both weight and newton contain a w. You only have weight while you're "wait"ing on Earth, but even "mass"tronauts have mass. Most physics problems use newtons (N) for weight, meters per second squared (m/s2) for gravitational force, and kilograms (kg) for mass. If you use a different unit for one of these values, you cannot use the same formula. Convert to scientific units before plugging them into the standard equation. These conversions may help you out if you're used to the imperial / U.S. system:  1 pound-force = ~4.448 newtons 1 foot = ~0.3048 meters If you're working on a complex problem, keep track of the units as you work through your solution. Remember that 1 newton is equivalent to 1 (kg*m)/s2. If necessary, make that substitution to help you cancel out units.  Example problem: Jeffrey weighs 880 newtons on Earth. What is his mass? mass = (880 newtons)/(9.8 m/s2) mass = 90 newtons/(m/s2) mass = (90 kg*m/s2)/(m/s2) Cancel units: mass = 90 kg Kg is the expected unit for mass, so you arranged the problem correctly.
تجنب الخلط بين الكتلة والوزن. استخدم وحدات علمية. تعامل بوحدة نيوتن إذا واجهتك مشكلة.