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3 years ago

Why is the answer B for this question? I know acceleration should be negative down but I don't know the other two variables.

Physics

1 answer:

AnnZ [28]3 years ago

6 0

Answer:

Explanation:

Displacement, velocity, and acceleration are vectors: they have magnitude and direction.

The convention is that "down" is negative and "up" is positive.

Thus, if an object is higher than when it started, its displacement is positive. If it is lower, the displacement is negative.

If it is still going "up", its velocity is positive. If it is falling, its velocity is negative.

1. Displacement

The formula for vertical displacement is

Δy = v₀t - ½gt²

If v₀ = 30 m/s, t = 2 s, and g = 9.8 m·s⁻², then

$\begin{array}{rcl}\Delta y & = & 30 \times2 - \dfrac{1}{2}\times 9.8 \times2^{2}\\& = & 60 - 4.9 \times 4\\& = & 60 - 19.6\\& = & \mathbf{40.4}\\\end{array}\\\text{The displacement is}\textbf{ up}}$

2. Velocity

The formula for vertical velocity is

v = v₀ - gt

If v₀ = 30 m/s, t = 2 s, and g = 9.8 m·s⁻², then

$\begin{array}{rcl}v & = & 30 - 9.8 \times 2\\& = & 30 - 19.6\\& = & \mathbf{10.4}\\\end{array}\\\text{The velocity is}\textbf{ up}}$

3. Acceleration

The vertical acceleration is always -g = -9.8 m·s⁻².

The direction of the acceleration is down.

The only option with the sequence "up, up, down" is B.

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4 years ago

An airplane has a starting velocity of 300m/s. It then accelerates at a rate of 45m/s2 for a time of 10s. What is it's final vel

Olenka [21]

A = (v - u) / t

a = acceleration
v = final velocity
u = initial velocity
t = time

45 = (v - 300) / 10

45 × 10 = v - 300

450 + 300 = v

v = 750 m/s

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3 years ago

Consider the power dissipated in a series R–L–C circuit with R=280Ω, L=100mH, C=0.800μF, V=50V, and ω=10500rad/s. The current an

ki77a [65]

Answer:

0.28802

2.57162 W

14.28 W

53.55 W

6.07142 W

Explanation:

R = 280Ω

L = 100 mH

C = 0.800 μF

V = 50 V

ω = 10500rad/s

For RLC circuit impedance is given by

$Z=\sqrt{R^2+(X_L-X_C)^2}\\\Rightarrow Z=\sqrt{R^2+(\omega L-\dfrac{1}{\omega C})^2}\\\Rightarrow Z=\sqrt{280^2+(10500\times 100\times 10^{-3}-\dfrac{1}{10500\times 0.8\times 10^{-6}})^2}\\\Rightarrow Z=972.1483\ \Omega$

Power factor is given by

$F=\dfrac{R}{Z}\\\Rightarrow F=\dfrac{280}{972.1483}\\\Rightarrow F=0.28802$

The power factor is 0.28802

The average power to the circuit is given by

$P=\dfrac{V^2}{Z}\\\Rightarrow P=\dfrac{50^2}{972.1483}\\\Rightarrow P=2.57162\ W$

The average power to the circuit is 2.57162 W

Power to resistor

$P_R=IR\\\Rightarrow P_R=5.1\times 10^{-2}\times 280\\\Rightarrow P_R=14.28\ W$

Power to resistor is 14.28 W

Power to inductor

$P_L=IX_L\\\Rightarrow P_L=5.1\times 10^{-2}\times 10500\times 100\times 10^{-3}\\\Rightarrow P_L=53.55\ W$

Power to the inductor is 53.55 W

Power to the capacitor

$P_C=IX_C\\\Rightarrow P_C=5.1\times 10^{-2}\times \dfrac{1}{10500\times 0.8\times 10^{-6}}\\\Rightarrow P_C=6.07142\ W$

The power to the capacitor is 6.07142 W

8 0

3 years ago

Use the techniques to find the unit for speed

stellarik [79]

Answer:

The formula for speed is speed=distance

time

Explanation:

to work out what the units are for speed,you need to know the units for distance and time.In this example,distance is in metres(m) and time is in seconds (s) , so the units for speed is metre per second (m/s).

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4 years ago

Read 2 more answers

Water flows through a 2.5cm diameter pipe at a rate of

My name is Ann [436]

Answer:

From the Bernoulli energy principle,

ΔP + 1/2ρΔv² = 0 -------------------------- eqn 1

where

ΔP = pressure drop = P2 - P1 = (1 - 0.25)x10⁵ N/m =7.5 x 10⁴N/m

Δv²= velocity change = v₂² - v₁²

ρ = water density = 1kg/m3

Recall volumetric flow rate, Q=A v = constant

A = cross sectional area = πr²=πd²/4

d=pipe diameter at point 2 = 2.5cm = 0.025m and Q =0.20m³/min = 0.00333m³/s

So A= 0.000491m²

we can get v2 = Q/A = 6.79m/s

From eqn 1, v₁² = 2(P2 - P1)/ρ + v₂²

v₁² = (2 x 7.5 x 10⁴)/1000 + 6.79²

v₁² = 196

v₁ = 14m/s

we can now get the area of the constriction point 2, A₁ = Q/v₁

A₁ = 0.000238m² and the diameter now will be d₁

d₁² = 4 x A₁ / π

= 4 x 0.000238/3.14 = 0.000303m²

d₁ = √0.000303 = 0.0174m

Therefore, the diameter of a constriction in the pipe at the new pressure = 0.0174m = 1.74cm

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3 years ago