A lamp is suspended from the ceiling by two strings attached to different points, as shown. The lamp has a weight W. The weight of the lamp is 18 N. What is...
Question 1 Report
A lamp is suspended from the ceiling by two strings attached to different points, as shown. The lamp has a weight W.
The weight of the lamp is 18 N. What is the mass of the lamp if g = 9.0 N/kg?
Answer Details
The relationship between weight and mass is W = m g, which rearranges to m = W / g. The lamp has a weight of 18 N and the gravitational field strength is given as g = 9.0 N/kg. Substituting: m = 18 / 9.0 = 2.0 kg.
The two strings and the ceiling are distractors in this question. Regardless of how the lamp is supported, its weight is still 18 N and the relationship W = m g still applies. A common error is to multiply weight by g instead of dividing, which would give 162 kg. Another mistake is to simply divide by 10 instead of 9.0, or to confuse the weight value with the mass value. Always check that your answer has sensible units and magnitude: a household lamp with a mass of 2.0 kg is reasonable, whereas 162 kg is not.
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