A parcel hangs from a newton meter inside a lift. The lift is stationary and the reading is 45 N. What is the mass of the parcel? Take g = 9.0 N/kg.
Question 1 Report
A parcel hangs from a newton meter inside a lift. The lift is stationary and the reading is 45 N.
What is the mass of the parcel? Take g = 9.0 N/kg.
Answer Details
The newton meter reads 45 N when the lift is stationary, which means the weight of the parcel is 45 N (no acceleration, so the reading equals the true weight). To find mass from weight, rearrange W = m g to give m = W / g. Substituting: m = 45 / 9.0 = 5.0 kg.
A frequent error is to divide by 10 instead of 9.0, which would give 4.5 kg. Another mistake is to multiply weight by g, producing 405 kg, which is clearly unreasonable for a parcel. When a lift is stationary, there is no net acceleration, so the apparent weight shown on the meter equals the actual gravitational weight. If the lift were accelerating, the reading would differ from the true weight, but that is not the case here.
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