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Vladimir79 [104]
3 years ago
13

A weight lifter lifts a 345 N set of weights from ground level to a position over his head, a vertical distance of 1.89 m. How m

uch work does the weight lifter do, assuming he moves the weights at constant speed?
Physics
1 answer:
Pavlova-9 [17]3 years ago
3 0

Answer:652.05 J

Explanation:

Given

Weight of lifter W=345 N

vertical distance move h=1.89 m

Work done in lifting the weight is equal change in Potential Energy of weight

Change in Potential Energy =m g h

\Delta PE=345 \times 1.89=652.05 J

therefore work done is equal to 652.05 J  

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baseball is hit into the air at an initial speed of 37.2 m/s and an angle of 49.3 ° above the horizontal. At the same time, the
Agata [3.3K]

Answer:

The average speed of the fielder is 5.24 m/s

Explanation:

The position vector of the ball after it was hit can be calculated using the following equation:

r = (x0 + v0 · t · cos α, y0 + v0 · t · sin α + 1/2 · g · t²)

Where:

r = position vector at time t.

x0 = initial horizontal position.

v0 = initial velocity.

t = time.

α = launching angle.

y0 = initial vertical position

g = acceleration due to gravity (-9.8 m/s² considering the upward direction as positive).

Please, see the attached figure for a graphical description of the problem.

When the ball is caught, its position vector will be (see r1 in the figure):

r1 = (r1x, 0.873 m)

Then, using the equation of the position vector written above:

r1x = x0 + v0 · t · cos α

0.873 m = y0 + v0 · t · sin α + 1/2 · g · t²

Since the frame of reference is located at the point where the ball was hit, x0 and y0 = 0. Then:

r1x = v0 · t · cos α

0.873 m = v0 · t · sin α + 1/2 · g · t²

Let´s use the equation of the y-component of r1 to obtain the time of flight of the ball:

0.873 m = 37.2 m/s · t · sin 49.3° - 1/2 · 9.8 m/s² · t²

0 = -0.873 m + 37.2 m/s · t · sin 49.3° - 4.9 m/s² · t²

Solving the quadratic equation:

t = 0.03 s and t = 5.72 s.

It would be impossible to catch the ball immediately after it is hit at t = 0.03 s. Besides, the problem says that the ball was caught on its way down. Then, the time of flight of the ball is 5.72 s.

With this time, we can calculate r1x which is the horizontal distance traveled by the ball from home:

r1x = v0 · t · cos α

r1x = 37.2 m/s · 5.72 s · cos 49.3°

r1x = 1.39 × 10² m

The distance traveled by the fielder is (1.39 × 10² m - 1.09 × 10² m) 30.0 m.

The average velocity is calculated as the traveled distance over time, then:

average velocity = treveled distance / elapsed time

average velocity = 30.0 m / 5.72 s = 5.24 m/s

8 0
3 years ago
A 20 liter cylinder of helium at a pressure of 150 atm and a temperature of 27ÁC is used to fill a balloon at 1.00 atm and 37ÁC.
djyliett [7]

<u>Answer</u>

D) 3100 Liters


<u>Explanation</u>

To get the volume if the balloon you need to use the combined equation of the low of gases.

P₁V₁/T₁ = P₂V₂/T₂

(20×150)/(27+273) = (1×V₂)/(37+273)

3000/300 = V₂/310

10 = V₂/310

V₂ = 10 × 310

    = 3100 Liters


7 0
3 years ago
Read 2 more answers
The more you heat an object, the
zhannawk [14.2K]
The answer is D.  The temperature obviously doesnt rise slower or faster, and if you are heating an object, it would make no sense to say that less heat is being transferred.
8 0
3 years ago
Read 2 more answers
A car moving west slows down from a velocity of 50 m/s to 20 m/s in 15 seconds. What is its acceleration?
velikii [3]
Vf = Vo + at

Vf = 20 m/s
Vo = 50 m/s
a = ? 
t = 15

Therefore

20 = 50 + 15a

20 - 50 = 15a

-30 = 15a

a = -30 / 15

a = -2 m/s²
6 0
3 years ago
What is the velocity of a car that travels -50 meters in 5 seconds then 10 meters in 5 seconds
diamong [38]

Answer:

2 m/s

Explanation:

The first part of the question the car is going in reverse or negative along the x axis. Then the second part the car is moving forward along the x axis. So the car would only have velocity in the current direction of movement. So our equation for velocity is as follows.

v = d/t

v = 10 m/5 s

v = 2 m/s

3 0
3 years ago
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