If an object has mass 70 kg, what is its weight near Earth's surface using g ≈ 9.8 m/s^2?

If an object has mass 70 kg, what is its weight near Earth's surface using g ≈ 9.8 m/s^2?

• A. 686 N
• B. 70 N
• C. 9.8 N
• D. 700 N

Answer: (A)

Weight is the gravitational force on an object, which equals F = m g. With a mass of 70 kg and g ≈ 9.8 m/s^2, the weight is 70 × 9.8 = 686 Newtons. So the object weighs 686 N. The Newton is the unit for force (kg·m/s^2). If you see the other numbers, they don’t match the definition: 70 N would require a much smaller g or mass, 9.8 N would be the weight of a 1 kg mass, and 700 N is a rounded estimate that loses precision from using 9.8 and 70.

Weight is the gravitational force on an object, which equals F = m g. With a mass of 70 kg and g ≈ 9.8 m/s^2, the weight is 70 × 9.8 = 686 Newtons. So the object weighs 686 N. The Newton is the unit for force (kg·m/s^2).

If you see the other numbers, they don’t match the definition: 70 N would require a much smaller g or mass, 9.8 N would be the weight of a 1 kg mass, and 700 N is a rounded estimate that loses precision from using 9.8 and 70.