Question

Lab 6- Linear Kinetics

1. Place a pencil or pen on a flat surface. Using your finger, push on the side of the pencil in the middle. What happens? Now, reset the pencil and push again, using the same amount of force, but this time about midway between the center and the end of the pencil What happens this time? Considering the two trials you just completed, what do you think is the "take home message" about the application of force?

2. A softball with a mass of 0.5 kg is thrown to a catcher at a velocity of 28 m/s. How much momentum does the ball have?

3. in #2 above, how much impulse is needed to stop the ball?

4. if the ball contacts the pitcher's glove for 1 second during the catch, how much average force must be applied by the glove?

5. A line backer and a receiver run into each other head on. After the hit, the players stay together in the attempted tackle. If the line backer has a mass of 120 kg and is moving at 8 m/s and the receiver has a mass of 80 kg and is moving at 10 m/s, what would be the resultant velocity and in what direction?

6. Your pal has decided to help you rearrange your living room. You ask her to move the couch. The couch is 490 N and the static friction between the couch and the carpet is 0.35 and the coefficient of dynamic friction between the couch and the carpet is 0.29. How much force must your friend exert to start the couch moving?

7. in #6, how much force is needed to keep the couch moving?

8. If a boxer's punch to an opponents chin caused the opponent's 6 kg head to accelerate at 10 m/s², how much force did he apply with his fist?

9. Think about your sport. What are the sources of friction present in your sport?

Answer 1

1. The take home message about the application of force is that the location of the transfer of force is extremely important. In the first trial the force resulted in strictly a translation of the pencil. But in the second, it results in a combination of rotation about the z-axis and a translation.
2. 
3. 14kg*m/s
4. 
5. The players' resultant velocity would be 8.8m/s in the direction that the linebacker was heading
6. 
7. 
8. 
9. Football. Cleats on the turf, shoulderpads contact, gripping the football, catching the football