This preview shows pages 1–7. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Forces and Motion Forces and Motion Newton Newton s Laws Review s Laws Review Newton Newton s Third Law s Third Law Hook Hook s Law s Law Springs Springs Lecture 8 Example: Predicting Motion Using Newton Example: Predicting Motion Using Newton s 2 s 2 nd nd A force acts on a 1.2 kg object which is initially at rest at the origin. (a) What is the objects acceleration? (b) What is its location after 3.5s ? (c) How fast and in what direction is it moving after 3.5s ? (a) From Newtons 2 nd the acceleration is: F 2.4 i 1.7 j a F / m 2.4 i 1.7 j /1.2 2.0 i 1.4 j m / s 2 (b) From the kinematics for an object with uniform acceleration the location is: r t v t 1 2 at 2 1 2 2.0 i 1.4 j t 2 r 3.5 1 2 2.0 i 1.4 j 3.5 2 12.25 i 8.68 j m Example: Predicting Motion Using Newton Example: Predicting Motion Using Newton s 2 s 2 nd nd A force acts on a 1.2 kg object which is initially at rest at the origin. (a) What is the objects acceleration? (b) What is its location after 3.5s ? (c) How fast and in what direction is it moving after 3.5s ? The objects speed after 3.5s is: F 2.4 i 1.7 j (c) From the kinematics for an object with uniform acceleration the velocity is: v t v at 2.0 i 1.4 j t v 3.5 2.0 i 1.4 j 3.5 7 i 5 j m / s v v x 2 v y 2 7 2 5 2 8.6 m / s Its direction (as measured from the x axis) is: tan 1 5 7 35.5 Example: Hockey Player and that Puck Example: Hockey Player and that Puck A hockey player strikes a 170g puck accelerating it from rest to 50 m/s . If the hockey stick is in contact with the puck for 2.5 ms , what is the average force on the puck? To find the average force we need the average acceleration: a v t 50 m / s 2.5 10 3 s 20 10 3 m / s 2 From Newtons 2 nd the average force is: F m a .17 kg 20 10 3 m / s 2 3.4 kN Example: A Truck and That Pole Example: A Truck and That Pole A truck moving at 70km/h collides with a pole. The front of the truck is compressed by .94m . What average force must a seatbelt exert in order to restrain a 75 kg passenger in this accident?...
View
Full
Document
This note was uploaded on 04/16/2008 for the course PHYS PHYS2A taught by Professor Hicks during the Spring '08 term at UCSD.
 Spring '08
 Hicks
 Force

Click to edit the document details