Question

1. when rowing a boat, a person does 15,000 joules of work every 60 seconds. (pay attention to the units)

a. calculate the power used to row the boat

b. calculate the work done to row the boat for 30 minutes
givens and unknowns
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equations and constants
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calculations

1. an elevator with 5 people has a mass of 1825 kg and is lifted 12 m vertically in 4.50 s.

a. calculate the force needed to lift the elevator

b. calculate the work done to move the elevator

c. calculate the power needed to move the elevator
givens and unknowns
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equations and constants
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Explanation:

Problem 6

Step1: Define power formula

Power $P = \frac{W}{t}$

Step2: Substitute values for part a

$W=15000\ \text{J}$, $t=60\ \text{s}$
$P = \frac{15000}{60} = 250\ \text{W}$

Step3: Convert time for part b

30 minutes = $30 \times 60 = 1800\ \text{s}$

Step4: Find work for part b

$W = P \times t = 250 \times 1800 = 450000\ \text{J}$

Step1: Calculate force (part a)

Force equals weight: $F = m \times g$, $g=9.8\ \text{m/s}^2$
$F = 1825 \times 9.8 = 17885\ \text{N}$

Step2: Calculate work (part b)

Work $W = F \times d$
$W = 17885 \times 12 = 214620\ \text{J}$

Step3: Calculate power (part c)

Power $P = \frac{W}{t}$
$P = \frac{214620}{4.50} = 47693.33\ \text{W}$

Answer:

a. $250\ \text{watts}$
b. $450000\ \text{joules}$

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Problem 7