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

2. 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)

3. Example: A car going 34 m/s hits a. 0025 kg bug. The collision lasts
Example: A car going 34 m/s hits a 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?)

4. Whiteboards
Ft = mv
1 | 2 | 3 | 4

5. 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

6. 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

7. 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

8. 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 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

9. 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