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Triss [41]
3 years ago
7

A sled of mass 8 kg slides along the ice. It has an initial speed of 4 m/s but

Physics
1 answer:
marysya [2.9K]3 years ago
6 0

As our story begins, the sled ... whose mass is 8 kg ...  is sliding along the ice at a speed of 4 m/s.

The sled's kinetic energy is (1/2 m v²) = (4 kg · 16 m²/s²) = 64 J .

After what seems like only the blink of an eye, the sled is no longer sliding.  It is stationary.  Motionless.  At Rest.  Just sitting there !  

Its speed has been reduced to zero and ... because kinetic energy is the energy of motion ... the sled's kinetic energy is now also zero.  Sixty-four Joules of energy have disappeared !

How can this be ? ! ? We know that energy is conserved.  It can never just appear out of nothing, and it can never just disappear into nothing.  If energy suddenly appears, it had to come from somewhere, and if energy suddenly disappears, it had to go somewhere.  So where did our 64 Joules of kinetic energy go ?

It went into the ice, THAT's where !  We can say that the sled did 64J of work, and melted a thin slick layer of water on the surface of the ice.  OR we can say that friction did NEGATIVE 64J of work on the sled, to cancel the 64J that it had originally, sap its kinetic energy, and bring it to rest.

I think <em>choice-B</em> was supposed to say "<em>B. -64J</em>", but somebody typed it sloppily and neglected to proofread it before posting.

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3 years ago
A skydiver jumps from an airplane that is moving at 50 meters per second at a height of 1,000 meters what describes the skydiver
kkurt [141]

Answer:

11060M  Joules, where M is the mass of the diver in kg

Explanation:

Mass of the skydiver missing, we're assuming it's M.

It's total energy is the sum of the contribution of his kinetic energy (K)- since he's moving at 50 m/s, and it's potential energy (U), since he's subject to earth gravity.

Energy is the sum of the two, so E = K+U= \frac 12 M v^2 + Mgh = M (\frac 12 \cdot 50^2 + 9.81\cdot 1000) = M ( 1250 + 9810) = 11060\cdot M

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2 years ago
A swimmer is swimming to the left with a speed of 1.0 m/s when she starts to speed up with constant acceleration. The swimmer re
kolezko [41]

Answer:

Correct answer: t = 2.86 seconds

Explanation:

We first use this formula

V² - V₀² = 2 a d    

where V is the final velocity (speed), V₀ the initial velocity (speed),

a the acceleration and d the distance.

We will calculate the acceleration from this formula

a = (V² - V₀²) / (2 d) = (2.5² - 1²) / (2 · 5) = (6.25 - 1) / 10 = 5.25 / 10

a = 0.525 m/s²

then we use this formula

V = V₀ + a t  => t = (V - V₀) / a = (2.5 - 1) / 0.525 = 1.5 / 0.525 = 2.86 seconds

t = 2.86 seconds

God is with you!!!

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