Force time mass and velocity Contents New concept

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. 020 seconds. What force does the windshield exert on the bug? 1. F t = m v 2. (F )(. 02 s) = (. 0025 kg)(34 m/s) 3. F = (. 0025 kg)(34 m/s)/(. 02 s) 4. F = 4. 25 N (units? )

Whiteboards Ft = mv 1|2|3|4

What force for 10. seconds makes a 2. 0 kg rocket speed up to 75 m/s from rest? (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. 10 seconds. What is the ball’s change in velocity? (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. It speeds up from rest to. 25 m/s. What is the mass of the set? (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 x 102 kg 6. 0 x 102 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. 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

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