A 60-kg woman runs up a flight of stairs having a rise of 4 meters in a time of

Question

A 60-kg woman runs up a flight of stairs having a rise of 4 meters in a time of 4.2 seconds. What average power did she supply? A) 616 W B) 1232 W C) 560 W D) 380 W E) 672 W A 10.0 kg box starts at rest and slides 3.5 m down a ramp inclined at an angle of 10 degree with the horizontal. If there is no friction between the ramp and crate, what is the velocity of the crate at the bottom of the ramp? (g = 9.8 m/s^2) A) 10.7 m/s B) 2.7 m/s C) 3.5 m/s D) 6.1 m/s E) 8.3 m/s A bullet moving at a speed of 150 m/s passes through a plank of wood at 130 m/s. Another bullet moving at 80 m/s passes through the same plank at what speed? A) 60m/s B) 44 m/s C) 22m/s D) 28 E) 35 m/s

Explanation / Answer

17. P=W/t = mgh/t = (60*9.8*4)/4.2 = 560 W

18. KEf = PEi

1/2mvf^2 = mgh

1/2vf^2 = gdsin

1/2*vf^2 = 9.8*3.5*sin10    => vf= 3.45 m/s

19. KEi = Wfriction + KEf

1/2mvi^2 = Wfriction + 1/2mvf^2

Wfriction = 1/2mvi^2 - 1/2mvf^2

Wfriction /m = 1/2vi^2 - 1/2vf^2 = ½*150^2 – ½*130^2 = 2800 J/kg

When vi=80m/s

1/2mvi^2 = Wfriction + 1/2mvf^2

1/2vi^2 = Wfriction /m + 1/2vf^2

½*80^2 = 2800 + 1/2vf^2    => vf=28.3 m/s

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.