N1-6 Test results 120 – 155 – 3 students 119 – 100 – 5 students 82 – 100 – 2 students

Chapter N10 Assigned Problems N10B.3, B.6, S.4, S.7

The principles of projectile motion The horizontal motion should be treated separately from the vertical motion. The vertical motion is used to determine the time the projectile will be in the air The horizontal motion will be used to determine the distance the projectile travels.

Ex. A girl runs 8 m/s off a dock 1.5 m above the water. Step 1. Calculate how long it will take her to fall the 1.5 m. (Note that this does not depend on how fast she is running) z = 1.5 m, a = 9.8 m/s 2, t = ? z=z 0 +v 0,z t+½a z t 2

How far from the end of the dock does she hit the water. She is in the air seconds Each second she travels 8 m. She hits the water 4.43 m from the end of the dock.

A ball is hit with a velocity of 30 m/s at an angle of 40º on level ground. How far will it travel? v0v0 v 0z v 0x θ v 0x =v 0 cosθ v 0z =v 0 sinθ v 0x =30 m/s cos(40º)=23 m/s V 0z =30 m/s sin(40º)=19.3 m/s

The principle here is the same, use motion in the z direction to determine the time in the air and motion in the x direction to determine the distance. v z =v 0z +at, a= m/s 2, v 0 =19.3 m/s An object shot straight in the air with a velocity of 19.3 m/s will stay in the air 2 x 1.97 sec (it must go up then fall back down) = 3.94 seconds The velocity in the x direction is 23 m/s so in 3.94 seconds it will travel 90.6 m.

A complete printout of your scores is in your folders. – There is a sheet of paper on the front desk on which you should write any problems that you have with the printout labs or problems turned in for which you do not have credit, etc. We will have one more lab – tomorrow then spend all of our time reviewing. –The best review is for you to work the problems on the practice test and discuss where you get stuck. The final exam will be 8:00 am Wednesday, Dec. 5. Students who arrive later than 8:30 will have their grades lowered.

There is no limit to how much the final can raise your grade (anyone who does well enough on the final will receive an “A”. Doing poor on the final could lower you grade – but in past years this has been very rare. Work the problems on the practice exam and have me check your answers. This is the best way to review. Spend some time on your info sheet.

A ball is hit with a velocity of 30 m/s at an angle of 40º from the top of a hill that is 20 m high. How far will it travel in this case? This problem is something like the rocket we shot into the air in chapter N6. We need to calculate the time to the top of the path, then the height to which it raises (to which we must add the extra 20 m it will fall on the way down.) We already calculated the time to the top of the path = 1.97 seconds.

Calculation of the maximum height. z=z 0 +v 0,z t+½a z t 2, z 0 = 20 m, v 0z =19.3 m/s, t = 1.97 s, a = m/s 2 z=39 m The time to fall 39 m is given by So the total time in the air is 1.97 s s = 4.79 s The distance is v 0x t = 23 m/s ·4.79 s = m

Problems N10B.3, B.6, S.4, S.7