Relative Motion

Outline

• Example

Remember

Rrr

Vvv

aa

Ex 1: Two cars are moving towards one another. Car 1 is moving at v1=20m/s and Car 2 at v2=30m/s.

a) What is the relative speed between the cars ?

b) How does it differ if Car 1 was stationary and Car 2 moving at 50m/s ?

Ex 2: The cops are chasing a bank robber. Driving at 50m/s they fire a bullet to shoot out his tire. If the gun fires the bullet at 300m/s, what is the bullet’s speed as measured by a TV camera crew parked beside the road?

Ex 3: The cops are chasing a bank robber. Driving at 50m/s they fire a bullet to shoot out his tire. If the gun fires the bullet at 300m/s, and the bank robbers are getting away at 60m/s, what is the speed of the bullet with respect to their car is it goes by them?

Ex 4: A boat takes 3.0h to travel 30km down the river and 5.0h to return. How fast is the river flowing ?

Ex 5: A rescue plane is flying 500m above ground level at a speed of 40m/s.

a) Where, relative to a group of stranded hikers below, should it drop the parcel so that it lands at their position?

b) Where will the parcel land with respect to the plane ?

For Next Class

• Read 12.3-12.4

Try Chapter 6 # 14, 15, 17