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Anuta_ua [19.1K]
3 years ago
9

A rope exerts a force F on a 20.0-kg crate. The crate starts from rest and accelerates upward at 5.00 m/s2 near the surface of t

he earth. What is the kinetic energy (in J) of the crate when it is 4.0 m above the floor?
Physics
1 answer:
tia_tia [17]3 years ago
5 0

Answer:

400 J

Explanation:

Given:

Δy = 4.00 m

v₀ = 0 m/s

a = 5.00 m/s²

Find: v²

v² = v₀² + 2aΔy

v² = (0 m/s)² + 2 (5.00 m/s²) (4.00 m)

v² = 40.0 m²/s²

Find KE:

KE = ½ mv²

KE = ½ (20.0 kg) (40.0 m²/s²)

KE = 400 J

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Alex_Xolod [135]

Answer:

-4.5 m/s

Explanation:

Even without doing calculations, we know that a projectile has the same speed coming down as it did going up at the same height.  Since it went up at 4.5 m/s, it returns down at -4.5 m/s.

To prove it with math, use the given information:

v₀ = 4.5 m/s

a = -9.8 m/s²

Δy = 0 m

Find: v

v² = v₀² + 2aΔy

v² = (4.5 m/s)² + 2 (-9.8 m/s²) (0 m)

v = -4.5 m/s

3 0
4 years ago
Explain why color is a measure of a star’s temperature.
guajiro [1.7K]

Answer: The color of a star plays a significant role in determining its age as well as its temperature. A star normally appears to be shining as we see through the atmosphere. An increase in the temperature of a star releases more energy and this can be observed in the various colors of color spectrum.

The hottest star generally appears to be bluish-white in color whereas the coldest star usually appears to be reddish in color.

Thus, a star's color can help us determining its temperature.

3 0
3 years ago
Lily took 6 hours to complete a journey at an average speed of 58 km/h. For the first 4 hours, she travelled at an average speed
arlik [135]

Answer:

92km

Explanation:

Given parameters:

Duration of the journey  = 6hrs

Average speed  = 58km/hr

  Now, let us find the total distance of the journey;

 Distance  = Speed x time

  Distance  = 58 x 6   = 348km

So;

 Average speed for the first 4hrs  = 64km/hr

                                               Time  = 4hrs

     Distance  = 64 x 4 = 256km

For the rest of the journey, the student will cover;

                               = 348km  - 256km

                               =  92km

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