Force, time, mass, and velocity Contents: New concept Example Whiteboards: 1,2,3,4

Force, time, mass, and velocity So far we have: p = mv, so p = mv And Impulse = p = Ft Impulse = F t = mv F = Force (N) t = Elapsed time (s) m = Mass (kg) v = Change in velocity (m/s)

Example: A car going 34 m/s hits a. 0025 kg bug. The collision lasts Example: A car going 34 m/s hits a .0025 kg bug. The collision lasts .020 seconds. What force does the windshield exert on the bug? F t = mv (F )(.02 s) = (.0025 kg)(34 m/s) F = (.0025 kg)(34 m/s)/(.02 s) F = 4.25 N (units?)

Whiteboards Ft = mv 1 | 2 | 3 | 4

What force for 10. seconds makes a 2 What force for 10. seconds makes a 2.0 kg rocket speed up to 75 m/s from rest? 15 N (m)(v) = (F )( t) (2.0 kg)(75 m/s) = (F )(10 s) F = (2.0 kg)(75 m/s)/(10 s) = 15 N

A baseball bat exerts a force of 200. N on a. 50 kg ball for A baseball bat exerts a force of 200. N on a .50 kg ball for .10 seconds. What is the ball’s change in velocity? 40. m/s (m)(v) = (F )( t) (.50 kg)(v) = (200. N )(.10 s) v = (200. N )(.10 s)/(.50 kg) = 40. m/s

Jolene exerts a 50. N force for 3. 00 seconds on a stage set Jolene exerts a 50. N force for 3.00 seconds on a stage set. It speeds up from rest to .25 m/s. What is the mass of the set? 6.0x102 kg (m)(v) = (F )( t) (m)(.25 m/s) = (50. N )(3.0 s) m = (50. N )(3.0 s)/(.25 m/s) = 600 kg = 6.0 x102 kg

For what time must a 517 kg spaceship fire its retro rockets to slow it from 576 m/s to 312 m/s. The rockets generate 35,000 N of thrust. 3.9 seconds v = 576 m/s - 312 m/s = 264 m/s (517 kg)(264 m/s) = (35,000 N )( t)  t = (517 kg)(264 m/s)/(35,000 N ) = 3.9 seconds

If we re-arrange things in m v = F  t Now v = acceleration, so t One last thing: If we re-arrange things in m v = F  t t t Now v = acceleration, so t Which gives us F = m v = ma = p t t