{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Chapter_6Solns

# Chapter_6Solns - Solutions to Assigned Problems Unit 3...

This preview shows pages 1–4. Sign up to view the full content.

1 Solutions to Assigned Problems, Unit 3, Chapter 6 CONSERVATION OF ENERGY 1. Strategy Use Eq. (6-1). Solution Find the work done by Denise dragging her basket of laundry. cos (30.0 N)(5.0 m)cos60.0 75 J WF r θ = ° = x 30.0 N 60.0° 5.0 m 5. Strategy Use Newton’s second law and Eq. (6-2). Solution Find the net force on the barge. sin sin 0 and cos cos . yx x F TT F T T F θθ Σ =−= Σ =+ = Find the work done on the barge. (2 cos ) 2(1.0 kN)cos45 (150 m) 210 kJ x WFx T x = Δ = ° = 1.0 kN 45° 150 m y x 45° 1.0 kN 9. Strategy Use Eq. (6-2). Let the x -axis point in the direction of motion. Solution The force of friction is opposite the motion of the box, and according to Newton’s second law, it is equal to kk k . f Nm g μμ == Juana’s horizontal force is in the direction of motion. Solve for the displacement. 2 , so 74.4 J 1.3 m . 124 N 0.120(56.8 kg)(9.80 m s ) x x WFx WW W x FF fF m g μ Δ= = = = = −− N m g x f k F 13. Strategy The kinetic energy of the sack is equal to the work done on it by Sam. Use Eqs. (6-2), (6-6), and (6-7). Solution (a) Compute the kinetic energy of the sack. 22 2 fi 11 ( ) 0 , so (2.0 N)(0.35 m) 0.70 J . x Km vv m v K W F xK = −= = = Δ = = (b) Solve for the speed of the sack. 2 1 2 2(0.70 J) 0.37 m s . 2 10.0 kg K v v m 17. Strategy Use Eqs. (6-6) and (6-7). Solution Compute the work done by the wall on the skater. total f i 0 (69.0 kg)(11.0 m s) 4.17 kJ WK K K m v =Δ = = − =−

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Chapter 6: Conservation of Energy College Physics 2 25. Strategy Use Newton’s second law and Eq. (6-10). Solution The total work is given by total vs. friction vs. gravity . WW W = + Find the work done against friction. cos 0, y FN m g φ Σ=− = so cos . fNm g μ μφ == 2 22 vs. friction cos 1 Lh L Wf x m g L m g L m g h ⎛⎞ =Δ= = = ⎜⎟ ⎝⎠ and the work done against gravity is vs. gravity . Wm g h = So, total 4.0 m 1 1 (1400 N)(1.0 m) 0.20 1 1 2.5 kJ . 1.0 m L g h h =− + = + = 27. Strategy Use conservation of energy. Solution Find a general expression for the speed of the cart. 444 4 4i 11 , so , where 1, 2, or 3. nnn n n E K U mv mgy E E K U mv mgy n =+= + = + = Solve for . n v 222 fi 4 4 4 4 2 ( ). nn n n Em v m g y v m g yvvg y y =+ = = + Compute the speed at each position. 1 2 3 (15 m s) 2(9.80 m s )(20.0 m 0) 25 m s (15 m s) 2(9.80 m s )(20.0 m 15.0 m) 18 m s (15 m s) 2(9.80 m s )(20.0 m 10.0 m) 21 m s v v v = = = 29. Strategy Use conservation of energy. Solution Find the maximum height achieved by the swinging child. 2 f i i f top bottom top bottom 2 1 0, s o 2 (4.9 m s) 0.70 m 1.9 m . 2 2(9.80 m s ) KK m v UUm g y m g y v yy g −= =−= = + = 31. Strategy Assume frictional forces and air resistance are negligible. Use conservation of energy. Solution Find h , the highest position the car reaches above the bottom of the hill. 2 2 2i ii i 2 1( 2 0 . 0 m s ) 0, so 5.0 m 25 m . 2(9.80 m s ) v U mgh mgh K mv h h g Δ= = = += + =
College Physics Chapter 6: Conservation of Energy 3 33. Strategy Since energy is conserved and nonconservative forces do no work, . K U Δ =−Δ Let the y -axis point upward.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 7

Chapter_6Solns - Solutions to Assigned Problems Unit 3...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online