A crate moves 10 m to the right on a horizontal surface as a woman pulls on it w

Question

A crate moves 10 m to the right on a horizontal surface as a woman pulls on it with a 10-N force. Rank the situations shown below according to the work done by her force, least to greatest. 3, 2, 1, 1, 3, 2 1, 2, 3 2, 3, 1 2, 1, 3 An escalator is used to move 20 people (60 kg each) per minute from the first floor of a department store to the second floor, 5 m above. The power required is approximately: 200 W 60,000 W 100 W 1000W 2000 W A 40-N crate rests on a rough horizontal floor. A 12-N horizontal force is then applied to it If the coefficients of friction are mu_s = 0.5 and mu_k = 0.4. the magnitude of the frictional force on the crate is: 16 N 40N 12 N 8N 20 N A professor holds an eraser against a vertical chalkboard by pushing horizontally on it. She pushes with a force that is much greater than is required to hold the eraser. The force of friction exerted by the board on the eraser increases if she: stops pushing pushes so her force is slightly upward but has the same magnitude pushes so her force is slightly downward but has the same magnitude pushes with slightly less force pushes with slightly greater force

Explanation / Answer

12. work done = F .d      { dot product }

            = |F||d| cos@

@ is the angle between force and displacement vector.

1: @ = 0 deg => cos0 = 1

2: @ is in between 0 to 90 . cos@ < 1

3 :@ = 90 . cos90 = 0

Ans. 3 , 2 , 1

13. energy required to move 5 m above = m gh

       = 20 x 60 x 10 x 5 = 50000 J

Power = energy / time = 50000 / 60s =1000 W

Ans(D)

14. N = mg = 40 N

maximum static friction force, fmax = us N = 0.5 x 40 = 20 N

and applied force is less than fmax so block will not move

and friction force= F = 12 N

ANs(C)

15. ANs ( c)

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

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