Spring 2005

MWF 11:30

**Instructor**: Dr. Bruce Law, CW
327, Tel: 532-1618.

# ANSWERS TO REVIEW QUESTIONS OF Home
Work 2

# R5. Average speed = distance/time =
15km/0.5hr = 30km/hr

# R6. Distance = speed x time = 25km/hr x
0.5hr = 12.5km

# R8. Yes

# R9. Yes it maintains a constant speed. No it
does not maintain a constant velocity because it`s
direction is changing.

# R11. Acceleration = (change in
velocity)/time = 100km/h/10s = 10km/h/s.

# R12. Acceleration = 0km/h/s because it`s velocity is constant.

# R20. Velocity (after 5s) = g x time =
10m/s/s x 5s = 50m/s

# Velocity (after 6s) = 10m/s/s x 6s = 60m/s

# ANSWERS TO EXCERISES OF Home Work 2

# E3. Instantaneous speed.

## E4. The speed of both airplanes are the same and
equal to 300 km/h. However, their velocities are not the same - one is 300
km/h, North while the other is 300 km/h, South.

**E6. Yes, the
automobile in this case would be slowing down, i.e. decelerating. **

**E8. (a) Yes,
your velocity does change because your direction changes from north to east.
(b) Yes, you are accelerating because your velocity is changing. Recall
Acceleration = change in velocity/change in time. **

**E11. No, you don`t know if both cars accelerated over the same or
different periods of time.**

**(Recall that
acceleration = change in velocity/time.)**

**E14. (a) Yes,
if an object is moving at constant velocity then its acceleration is zero. (b)
Yes, eg. if you throw a ball
in the air, at the top of its flight, its speed is zero while its acceleration
due to gravity is still 10m/s/s, down. **

** **

# ANSWERS TO PROBLEMS OF Home Work 2

# P1. From v = d/t therefore t = d/v. We
convert 3m to 3000mm and therefore the time t = 3000mm/1.5mm/year = 2000 years.

**P2.
Acceleration = (final velocity - initial velocity)/time = (0 - 100 km/h)/10 s =
-10 km/h/s **

**P3. Since it
starts going up at 30m/s and loses 10m/s each second, its time going up is 3
seconds. Its time returning is also 3 seconds, so it`s
in the air for a total of 6 seconds. Distance up (or down) is 0.5gt**^{2}
= 5 x 3^{2} = 45m.

**P5.
Instantaneous velocity v = gt = 10m/s/s x 10s =
100m/s, down.**

**Average
velocity = (v**_{i} + v_{f})/2
= (0 + 100)/2 = 50m/s, down.

**Distance, d =
0.5gt**^{2} = 0.5 x 10 x 10^{2} = 500m