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Archy [21]
3 years ago
14

An athlete whose mass is 97.0 kg kg is performing weight-lifting exercises. Starting from the rest position, he lifts, with cons

tant acceleration, a barbell that weighs 420 N N . He lifts the barbell a distance of 0.65 m m in a time of 1.5 s s . Part A Use Newton's laws to find the total force that his feet exert on the ground as he lifts the barbell. Express your answer using two significant figures. F floor Ffloor = nothing N?
Physics
1 answer:
SIZIF [17.4K]3 years ago
6 0

Answer:

470 N.

Explanation:

Using equations of motion:

S = vi*t + 1/2*(a*(t^2))

Given:

S = 0.65 m

t = 1.5 s

vi = 0 m/s

0.65 = 1/2 * (a * (1.5)^2)

a = 1.3/2.25

= 0.578 m/s^2

Force = mass * acceleration due to gravity

= 92 * 0.578

= 53.16 N

Total force = 420 + 53.16

= 473.16 N

= 470 N.

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An aluminum-alloy rod has a length of 10.0 cm at 20°C and a length of 10.015 cm at the boiling point of water (1000C). (a) What
nikitadnepr [17]

Answer:

a.  9.99625 cm b. 68 °C

Explanation:

(a) What is the length of the rod at the freezing point of water (0 0C)?

Before we find the length of the rod, we need to find the coefficient of linear expansion, α = (L - L₀)/[L₀(T - T₀)] where L₀ = length of rod at temperature T₀ = 10.0 cm, T₀ = 20 °C, L = length of rod at temperature T = 10.015 cm and T = 100 °C

Substituting the values of the variables into the equation, we have

α = (L - L₀)/[L₀(T - T₀)]

α = (10.015 cm - 10.0 cm)/[10.0 cm(100 °C - 20 °C)]

α = 0.015 cm/[10.0 cm × 80 °C]

α = 0.015 cm/[800.0 cm °C]

α = 0.00001875 /°C

We now find the length L₁ at T₁ = 0 °C from

L₁ = L₀(1 + α(T₁ - T₀))

So, substituting the values of the variables into the equation, we have

L₁ = L₀(1 + α(T₁ - T₀))

L₁ = 10.0 cm[1 +  0.00001875 /°C(0° C - 20 °C)]

L₁ = 10.0 cm[1 +  0.00001875 /°C × -20° C]

L₁ = 10.0 cm[1 - 0.000375]

L₁ = 10.0 cm[0.999625]

L₁ = 9.99625 cm

(b) What is the temperature if the length of the rod is 10.009 cm?

With length L₃ = 10.009 cm at temperature T₃, using

L₃ = L₀(1 + α(T₃ - T₀))

making T₃ subject of the formula, we have

L₃/L₀ = 1 + α(T₃ - T₀)

L₃/L₀ - 1 = α(T₃ - T₀)

T₃ - T₀ = (L₃/L₀ - 1)/α

T₃ = T₀ + (L₃/L₀ - 1)/α

substituting the values of the variables into the equation, we have

T₃ = 20 °C + (10.009 cm/10.0 cm - 1)/0.00001875 /°C

T₃ = 20 °C + (1.0009 - 1)/0.00001875 /°C

T₃ = 20 °C + 0.0009/0.00001875 /°C

T₃ = 20 °C + 48 °C

T₃ = 68 °C

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Sitting in a chairlift, Rebecca has a gravitational potential energy of 5,997.6
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Answer:

B) 12 m

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5997.6 J = (51 kg) (9.8 m/s²) h

h = 12 m

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