PHYSICS 5A Lecture 10: 5A Lecture 10

Please, I need help! I don't understand how to do thisproblem.

A CD case slides along a floor in the positive direction of an xaxis while an applied force Fa acts on the case. The force isdirected along the x axis and has the x component Fax = 5.0x –4.0x^2, with x in meters and Fax in newtons. The case starts atrest at the position x = 0, and it moves until it is again at rest.(a) At what position is the work maximum, and (b) what is thatmaximum value? (c) At what position has the work decreased to zero?(d) At what position is the case again at rest?

Thank you in advance!

vf = vi + at
rx = vit + ½ at2
vf2 = vi2 +2arx
rx = ½ (vi + vf)t

4. A sailboat is moving across the water at 3.0 m/s. A gust of windfills its sails and it accelerates at a constant 2.0 m/s2. At thesame instant, a motorboat at rest starts its engines andaccelerates at 4.0 m/s2. After 3.0 seconds have elapsed, find thevelocity of (a) the sailboat, and (b) the motorboat.



7. A rail gun uses electromagnetic energy to accelerate objectsquickly over a short distance. In an experiment, a 2.00 kgprojectile remains on the rails of the gun for only 2.10x10-2 s,but in that time it goes from rest to a velocity of 4.00×103 m/s.What is the average acceleration of the projectile?



12. A space shuttle sits on the launch pad for 2.0 minutes, andthen goes from rest to 4600 m/s in 8.0 minutes. Treat its motion asstraight-line motion. What is the average acceleration of theshuttle (a) during the first 2.0 minutes, (b) during the 8.0minutes the shuttle moves, and (c) during the entire 10 minuteperiod? (be careful with min and seconds)



19. The United States and South Korean soccer teams are playing inthe first round of the World Cup. An American kicks the ball,giving it an initial velocity of 3.6 m/s. The ball rolls a distanceof 5.0 m and is then intercepted by a South Korean player. If theball accelerates at -0.50 m/s2 while rolling along the grass, findits velocity at the time of interception.




23. The city is trying to figure out how long the traffic lightshould stay yellow at an intersection. The speed limit on the roadis 45.0 km/h and the intersection is 23.0 m wide. A car istraveling at the speed limit in the positive direction and canbrake with an acceleration of -5.20 m/s2. (a) If the car is to stopon the white line, before entering the intersection, what is theminimum distance from the line at which the driver must apply thebrakes?



**(b) How long should the traffic light stay yellow so that if thecar is just closer than that minimum distance when the light turnsyellow, it can safely cross the intersection without having tospeed up?

I no this is alot of questions but im having trouble answeringthese! So please help me..