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nexus9112 [7]
3 years ago
14

A hand moves a block vertically upward. Its speed slows down as it moves up (it is decelerating). The work done by gravity on th

e block ____ if the system consists of the block only. The work done by gravity on the block ____ if the system consists of the block and the earth.
Physics
1 answer:
Nataly_w [17]3 years ago
5 0

Answer:

a. negative

b. zero

Explanation:

work is the change in the energy of a system due to external forces

work is done when a force moves a load through a distance in the direction of the force

The work done by a force on a  system is positive when the force  and the force displacement point  in the same direction and negative  when they point in opposite  directions

in the scenario we are considering in the question, the force (the hand) moves the block vertically upwards but the displacement of the block reduces (in the opposite direction) since it decelerates. as such the work done by gravity on the block is negative.

the work done on the block is zero if the system consists of the block and the earth because there is no gravitational force exerted on the system

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Let us consider two vectors A and B.

As per the question, the two vectors are perpendicular to each other.

Hence the angle between them  \theta =90 degree

We are asked to calculate the resultant of these two vectors.

As per parallelogram law of vector addition, the resultant of two vectors are-

                      R=\sqrt{A^{2}+ B^{2}+2ABcos\theta

                                =\sqrt{ A^{2}+ B^{2}+2AB*cos90}    [cos90=0]

                                =\sqrt{ A^{2}+ B^{2}

This is the way by which we can add two perpendicular vectors.


8 0
3 years ago
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Jaclyn plays singles for South's varsity tennis team. During the match against North, Jaclyn won the sudden death tiebreaker poi
Nataly [62]

Answer

given,

mass of ball, m = 57.5 g = 0.0575 kg

velocity of ball northward,v = 26.7 m/s

mass of racket, M = 331 g = 0.331 Kg

velocity of the ball after collision,v' = 29.5 m/s

a) momentum of ball before collision

   P₁ = m v

   P₁ = 0.0575 x 26.7

   P₁ = 1.535 kg.m/s

b) momentum of ball after collision

   P₂ = m v'

   P₂ = 0.0575 x (-29.5)

   P₂ = -1.696 kg.m/s

c) change in momentum

    Δ P = P₂ - P₁

    Δ P = -1.696 -1.535

    Δ P = -3.231 kg.m/s

d) using conservation of momentum

  initial speed of racket = 0 m/s

  M u + m v = Mu' + m v

  M x 0 + 0.0575 x 26.7 = 0.331 x u' + 0.0575 x (-29.5)

  0.331 u' = 3.232

     u' = 9.76 m/s

change in velocity of the racket is equal to 9.76 m/s

5 0
3 years ago
Martin has severe myopia, with a far point on only 17 cm. He wants to get glasses that he'll wear while using his computer whose
marusya05 [52]

Answer:

Explanation:

Far point = 17 cm . That means he can not see beyond this distance .

He wants to see at an object at 65 cm away . That means object placed at 65 has image at 17 cm by concave lens . Using lens formula

1 / v - 1 / u = 1 / f

1 / - 17 - 1 / - 65 = 1 / f

= 1 / 65 - 1 / 17

= -  .0434 = 1 / f

power = - 100 / f

= - 100 x .0434

= - 4.34 D .

6 0
3 years ago
We see a bolt of lightning and 4 s later we hear the thunderclap. If the speed of
Alex73 [517]

Answer:

i guess 0.8 miles away

Explanation:

mathematically:-

speed is given in question

Time is given

and we have to find distance

simply by using speed formula (s) = d/t

we get answer

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1 year ago
Which of the following is considered plagiarism?
-Dominant- [34]

Answer:

Copying materials from a source text, supplying proper documentation, but leaving out quotation marks

Explanation:

Plagiarism is when you take somebody's ideas and write them off as your own without giving them credit.

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3 years ago
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