Physics, 10.07.2019 06:30 jaythagod

Ariver has a steady speed 0.500 m/s. a student swims upstream a distance of1.00 km and swims back to the starting point. a) if the student can swim ata speed of 1.20 m/s in still water, how long does the trip take? b) how muchtime is required in still water for the same length swim? c) intuitively, whydoes the swim take longer when there is a current?

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Answer from: muravyevaarina

a) 33.6 min

b) 13.9 min

c) Intuitively, it takes longer to complete the trip when there is current because, the swimmer spends much more time swimming at the net low speed (0.7 m/s) than the time he spends swimming at higher net speed (1.7 m/s).

Explanation:

The problem deals with relative velocities.

Call Vr the speed of the river, which is equal to 0.500 m/sCall Vs the speed of the student in still water, which is equal to 1.20 m/sYou know that when the student swims upstream, Vr and Vs are opposed and the net speed will be Vs - VrAnd when the student swims downstream, Vr adds to Vs and the net speed will be Vs + Vr.

Now, you can state the equations for each section:

distance = speed × timeupstream: distance = (Vs - Vr) × t₁ = 1,000 mdownstream: distance = (Vs + Vr) × t₂ = 1,000 m

Part a). To state the time, you substitute the known values of Vr and Vs and clear for the time in each equation:

(Vs - Vr) × t₁ = 1,000 m(1.20 m/s - 0.500 m/s) t₁ = 1,000 m⇒ t₁ = 1,000 m / 0.70 m/s ≈ 1429 s(1.20 m/s + 0.500 m/s) t₂ = 1,000 m ⇒ t₂ = 1,000 m / 1.7 m/s ≈ 588 stotal time = t₁ + t₂ = 1429s + 588s = 2,017sConvert to minutes: 2,0147 s ₓ 1 min / 60s ≈ 33.6 min

Part b) In this part you assume that the complete trip is made at the velocity Vs = 1.20 m/s

time = distance / speed = 1,000 m / 1.20 m/s ≈ 833 s ≈ 13.9 min

Part c) Intuitively, it takes longer to complete the trip when there is current because the swimmer spends more time swimming at the net speed of 0.7 m/s than the time than he spends swimming at the net speed of 1.7 m/s.

Answer from: Quest

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.

Answer from: Quest

explanation:

there is no change in the electric potential energy as it is in rest on both conditions.

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Ariver has a steady speed 0.500 m/s. a student swims upstream a distance of1.00 km and swims back to...