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3 years ago

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In which of the following situations has work been done? Select one: a. A weightlifter holds a 50kg barbell over his head for 3

minutes. b. A yoga instructor holds a handstand for 1 minute. c. A man pulls against a stationary fire truck for 5 minutes. d. A child pushes a 2kg toy 10m across the floor.

1 answer:

Arlecino [84]3 years ago

5 0

Work done = Force * distance --- In other words, for work to be done, a force should be applied such that there is motion.

Therefore, the only situation meeting the criteria is situation d. where a force is applied resulting to motion.

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A runner is jogging in a straight line at a

Fiesta28 [93]

Answer:

Total distance traveled by bird is 10.5 km.

Explanation:

Given that,

Velocity of runner= 8.4 km/hr

Distance = 6.3 km

Velocity of bird = 42 km/hr

Suppose, How far does the bird travel?

We need to calculate the time of bird

Using formula of time

$t=\dfrac{d}{v_{b}}$

Put the value into the formula

$t=\dfrac{6.3}{42}$

$t=0.15\ hr$

We need to calculate the distance runner travels during time period

Using formula of distance

$d=v_{r}\times t$

$d=8.4\times0.15$

$d=1.26\ km$

We need to calculate the distance of runner to FL

Using distance

$d'=6.3-1.26$

$d'=5.04\ km$

We need to calculate the net closing speed between runner and bird

Using speed

$v'=v_{r}+v_{b}$

$v'=8.4+42$

$v'=50.4\ km/hr$

We need to calculate the time for runner and bird to meet

Using formula of time

$t=\dfrac{d}{v'}$

Put the value into the formula

$t=\dfrac{5.04}{50.4}$

$t=0.1\ hr$

We need to calculate the distance covered by runner

Using formula of distance

$d=vt$

Put the value into the formula

$d=8.4\times0.1$

$d=0.84\ km$

We need to calculate the distance covered by bird to runner

Using formula of distance

$d=vt$

Put the value into the formula

$d=42\times0.1$

$d=4.2\ km$

We need to calculate the total distance

Using distance

$D=6.3+4.2$

$D=10.5\ km$

Hence, Total distance traveled by bird is 10.5 km.

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3 years ago

What is the net force on an object<br> at rest?

Natasha2012 [34]

Answer:

Net force equals 0

Explanation:

Newton's first law states that an object at rest tends to remain at rest, and an object in motion tends to remain in motion with a constant velocity (constant speed and direction of motion), unless it is acted on by a nonzero net force. Note that the net force is the sum of all the forces acting on an object.

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4 years ago

Read 2 more answers

A refrigerator receives 240 V of electricity. If it uses 32 A of current, what is the resistance of the refrigerator?

Leokris [45]

$\mathfrak{\huge{\orange{\underline{\underline{AnSwEr:-}}}}}$

Actually Welcome to the Concept of the Ohms Law,

According to the Ohms law,

V = I*R, where, V = Voltage, I = Current, R = resistance,

so here given as, V = 240 V, I = 32 A,

so we get as, R = 240/32

R = 7.5 ohms,

===> The resistant R is ==> 7.5 ohms.

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3 years ago

Describe what has happened when a player "fumbles" the ball. (American Football)

Nesterboy [21]

Answer:

The players drops the ball either do to contact, the ball being stripped or personal error

Explanation:

6 0

3 years ago

(a) Calculate the self-inductance of a solenoid that is

adell [148]

Answer:

a) 0.142mH

b) 14mV

Explanation:

the complete answer is:

(a) Calculate the self-inductance of a solenoid that is <ghtly wound with wire of diameter 0.10 cm, has a cross-sec<onal area of 0.90 cm2 , and is 40 cm long. (b) If the current through the solenoid decreases uniformly from 10 to 0 A in 0.10 s, what is the emf induced between the ends of the solenoid

a) the self inductance of a solenoid is given by:

$L=\frac{\mu_o N^2 A}{L}$

μo: magnetic permeability of vacuum = 4\pi*10^{-7}N/A^2

A: cross sectional area = 0.9cm^2=9*10^{-5}m

L: length of the solenoid = 40cm = 0.4m

The N turns of the wire is calculated by using the diameter of the wire:

N = (40cm)/(0.10cm)=400

By replacing in the formula you obtain:

$L=\frac{(4\pi *10^{-7}N/A^2)(400)^2(9*10^{-5}m^2))}{(0.4m)}=1.42*10^{-4}H$

the self inductance is 1.42*10^{-4}H = 0.142mH

b) to find the emf you can use:

$emf=L\frac{\Delta I}{\Delta t}=(1.42*10^{-4}H)\frac{10A-0A}{0.10s}=0.014V=14mV$

the emf induced is 14mV

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3 years ago