A workman drops a wrench from the 12th floor of a building. Each floor is 3.0m tall.?
回答 (2)
2016-05-30 9:34 am
Take g = 9.81 m/s²
Take all downwards quantities to be positive.
s = 3.0 × (12 - 5) = 21.0 m
vₒ = 0 m/s
a = 9.81 m/s²
s = vₒt + (1/2)at²
21.0 = 0 + (1/2) × 9.81 × t²
t = √(21.0 × 2 / 9.81) s
Time taken, t = 2.1 s
Take all downwards quantities to be positive.
s = 3.0 × (12 - 5) = 21.0 m
vₒ = 0 m/s
a = 9.81 m/s²
s = vₒt + (1/2)at²
21.0 = 0 + (1/2) × 9.81 × t²
t = √(21.0 × 2 / 9.81) s
Time taken, t = 2.1 s
2016-05-30 9:36 am
Use the general equation for distance with uniform acceleration: x = x₀ + v₀t + ½at².
The wrench falls 7 floors = 21 m, so x = 21 m.
x₀ = 0 m; v₀ = 0 m/s; a = g = 9.8 m/s², so we have
21 m = 0 m + (0 m/s)t + ½(9.8 m/s²)t², or
(4.9 m/s²)t² = 21 m, or
t² = 21/4.9 s², so
t = 2.07 s. For 2 significant figures, round this to 2.1 s.
The wrench falls 7 floors = 21 m, so x = 21 m.
x₀ = 0 m; v₀ = 0 m/s; a = g = 9.8 m/s², so we have
21 m = 0 m + (0 m/s)t + ½(9.8 m/s²)t², or
(4.9 m/s²)t² = 21 m, or
t² = 21/4.9 s², so
t = 2.07 s. For 2 significant figures, round this to 2.1 s.
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