Set6_Lecture_10_22_2007

1 20 m 2 30 m 3 40 3 40 m 4 60 m 5 80 m f d wnet

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Unformatted text preview: both cases. 1) 20 m 2) 30 m 3) 40 3) 40 m 4) 60 m 5) 80 m F d = Wnet = ΔKE = 0 – 1/2 mv2 thus: |F| |F| d = 1/2 mv2 Therefore, if the speed doubles doubles, the stopping distance gets four times larger. times larger ConcepTest ConcepTest 6.4 Speeding Up A car starts from rest and accelerates to 30 mph. Later, it gets on a highway and accelerates to 60 mph Which takes more accelerates to 60 mph. Which takes more energy, the 0→30 mph, or the 30→60 mph? 1) 0 → 30 mph 2) 30 → 60 mph 30 3) both the same ConcepTest ConcepTest 6.4 Speeding Up A car starts from rest and accelerates to 30 mph. Later, it gets on a highway and accelerates to 60 mph Which takes more accelerates to 60 mph. Which takes more energy, the 0→30 mph, or the 30→60 mph? 1) 0 → 30 mph 2) 30 → 60 mph 30 3) both the same The change in KE (1/2 mv2 ) involves the velocity squared. velocity So in the first case, we have: 1/2 m (302 - 02) = 1/2 m (900) 1/2 In the second case, we have: 1/2 m (602 - 302) = 1/2 m (2700) 1/2 Thus, the bigger energy change occurs in the second case case. FollowFollow-up: How much energy is required to stop the 60-mph...
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This note was uploaded on 10/02/2010 for the course PHYS 1301 taught by Professor Ordonez during the Fall '09 term at University of Houston.

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