Basically if an object has mass and is moving it has what is termed momentum. How would the momentum of an object change if:

Transcription

1 Momentum Unit A General Outcome 1 Define momentum as a vector quantity equal to the product of the mass and the velocity of an object Basically if an object has mass and is moving it has what is termed momentum = Momentum is a Vector p = momentum m= mass v = velocity How would the momentum of an object change if: (a) The mass is doubled and velocity stays same (b) The velocity reduced by a factor of (1/3) (c) The direction change is from [E] to [W] Concept Check 1

2 Example What is the momentum of a 10 kg object travelling at 15 m/s [E]? Click the pic for another example Example The combined mass of a bobsled and two riders is 380 kg. The sled rider system has constant momentum of 4.68 X 10 3 kgm/s [W]. Calculate the velocity of the sled. solution Example During liftoff a model rocket's momentum increases by a factor of 4, while its mass decreases by a factor of a half. The velocity of the rocket was intially 8.5 m/s [up]. What is the final velcity during that time interval? hint erase Re arrange the formula for v, and then use the factors given in the question, to find the factor change of the velocity bring silly putty next day Page 453 questions! End day 1 2

3 Basics of Momentum Grade:«grade» Subject:«subject» Date:«date» 3

4 1 A D B C A 2.00 kg cannonball is fired out of a cannon at an angle of 30.0 to the horizontal. When the cannonball reaches the top of its path, its momentum has a magnitude of 800 kg m/s. What was the horizontal component of the cannonball's momentum when it left the cannon? A. 461 kg m/ s B. 800 kg m/s C. 924 kg m/s D kg m/s 4

5 Which of the following quantities is a scalar quantity? 2 D A C B A. Force B. Power C. Impulse D. Momentum 5

6 3 A D C B 6

7 Impulse and Momentum explain, quantitatively, the concepts of impulse and change in momentum, using Newton's laws of motion This is an interesting concept Newton began his work actually not by thinking about his famous equation F = ma. Instead he was more concerned with Force being defined as the rate of change of an object momentum with the passage of time. According to the following equation Now this can be re worked to say This can be a useful equation! It helps explain the situation when a hockey puck has aboslutely no momentum until a hockey stick wacks it for a period of time. The stick applies a force to the puck for a small interval of time and this is referred to as impulse (Impulse causes a change in momentum) 7

8 Impulse = FΔt Impulse has units of (N s) OR Impulse = change in momentum Impulse has units of (kgm/s) Consider a Bungee Jumper: Why would you want to use an elastic rope (stretchy one) vs Yellow rope tied around your waist? Example #1 To improve the safety of motorists, modern cars are built with front end crumple zones {the front end crumples upon impact}. A 1200 kg car traveling at constant velocity of 8.0 m/s [E], hits a wall and comes to a stop in 0.25s. 8.0 m/s [E] a) Calculate the impulse provided to the car b) What is the average net force exerted on the car? c) For the same impulse, suppose the car did not have a crumple zone, it had a rigid bumper. Now the car comes to a stop in 0.04s. Calculate the new force on the car 8

9 A Snowball B solution 9

10 Example #2 The graph below approximates the force applied to a tennis ball by a tennis racket during the time they are in contact. What impulse does the ball receive from the racket? Force (N) (0.5,10) Time (s) (1,0) HINT 10

11 Example #3 The net impulse delivered to the ball from t = 0.0 s to t = 6.0 s is A. 24N s B. 28 N s C. 32 N s D. 48 N s 11

12 Example #4 The club face of a golf club exerts an average force of 595 N on a golf ball while in contact with the ball. If the ball and club face are in contact for s, what is the impulse given to the golf ball by the club? A. 1.6 kg m /s in the direction of the golf club's movement B. 2.2 N s in the opposite direction of the golf club's movement C. 2.2 kg m/s in the direction of the golf club's movement D. 1.6 x 10 5 N s in the opposite direction of the golf club's movement 12

13 Look at these situations with your partner get some answers In two minutes you will be asked to share with your partner Greatest velocity change? Greatest acceleration? Greatest momentum change? Greatest Impulse? HINT 13

14 Do you really understand it? 14

15 WHY? Think, and discuss with your partner do you get it? The risk of a motorist becoming fatally injured in a vehicle collision is reduced when an airbag or a seatbelt is used because the airbag or seatbelt i change in momentum by ii the stopping force the motorist experiences. The statement above is completed by the information in row A 15

16 A B after 16

17 Bonus Project Anyone Extra Practice PAGE

18 Another Example solution click to go back 18

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