# The Physical World I

Spring 1999
MWF 11:30

Instructor: Dr. Amit Chakrabarti, CW 213, Tel: 532-1625.

# Home Work 2

## Conceptual Questions

1. One airplane travels due north at 300km/h while another one travels due south at 300 km/h. Are their speeds the same ? Are their velocities the same ? Explain.
2. Can an automobile with a velocity toward the north have an acceleration toward the south ? Explain.
3. You are driving north on a highway. Then, without changing speed, you round a curve and drive east. (a) Does your velocity change ? (b) Do you accelerate ? Explain.
4. Starting from rest, one car accelerates to a speed of 50 km/h, and another car accelerates to a speed of 60 km/h. Can you say which car underwent the greater acceleration ? Why or why not ?
5. (a) Can an object be moving when its acceleration is zero ? If so, give an example. (b) Can an object be accelerating when its speed is zero ? If so, give an example.
6. What happens to the acceleration of a ball in free fall if its mass is doubled ?
7. Two balls have the same size but are made from different materials: one from rubber and the other from iron. How do their acceleration compare in free fall ?
8. How (if at all) does the acceleration of a ball thrown upward differ from one that is dropped ?

## Problems

1. Which (if either) has the greater average speed, a car that travels from mile-post 93 to mile-post 98 in 5 minutes, or one that travels from mile-post 493 to mile-post 498 in 5 minutes ?
2. A race car accelerates from 54 m/s to 58 m/s in 2 sec. A runner accelerates 0 to 5 m/s in 2 seconds. Which has the larger acceleration ?
3. What is the acceleration of a vehicle that changes its velocity from 30 m/s, north to a dead stop in 10 sec ?
4. A racing car moving at 10 m/s, north increases its velocity to 16 m/s, north in a time interval of 3 sec. What is the average acceleration during this time interval ? What is the direction of this acceleration ?
5. A plane flies 600 km away from its base at 200km/h, then flies back to its base at 300 km/h. What is its average speed ?
6. A trucker drives a distance of 300 km between noon and 4 P.M. What was the average speed of the truck during this time ? Can you figure out the speed of the truck at 2 P.M. ?