Section 4: Answers

Hey, guys.
Section 4 was all about work and energy -- let me know if you have questions -- Some of these are SUPER hard!



1. Proof by drawing
2.(a) 72 J (b)-48 J.(c) = 24 J.
3. thought experiment.
4. thought experiment
5. (a)48 J(b) 0 (c) 0(d) - 40 J(e) 8 J.
6. work done by gravity 3.35 x 10^-2 J.Work by frictional force of air =-3.35 x 10^-2 J.
7. 51 x 10² J.
8. (a) 8.0 N (b)120 J.(c) 0. (d) -48 J.(e) -32 J.(f) 40 J.(g) 2√10 m/s.
9. (a) 19 N (b) -76 J(c) 96 J(d) 0(e) 0(f) 20 J(g)2√5 m/s.
10. (a) 10 J.(b) -10 J.(c) explain...(d) 0
11. (a)12 J.(b) -10 J.(c) explain(d) work energy theorem.
12. (a) -216 J.(b) 8.0 m/s.(c) 8.3 m
13.(a) Fnet=0 (b) = 29 J(c) 26 J.
14. 2.5 N
15. 21.7 x 10^-19 J.
16. (a) 800 N(b) 40 J. (c) 40J.(d) 0.05 m.
17. (a) 1(b) 0 (c) 1(d) 0(e) -2 J
18. 7.7 m/s
19. (repeating #18, now with friction) 6.3 m/s
20. (a)12.0 J. (b)4.0 J.(c) 1.6 kg. (d) √ 5 m/s.
21.(a) = 5R/2. (b) 3 mg
22. 4 m/s
23. (a) (2gL)^1/2 (b)T = 5mg(c) -mgL (d) -2mgL