Dec 3rd 2012, 03:10 PM #1 Junior Member   Join Date: Dec 2012 Posts: 7 hey please help me with this ( mechanics) (1) If you pull horizontally on a crate with a force of 200N , it slides across the floor in dynamic equilibrium .How much friction is acting on the crate ? 200N (2) One airplane travels due north at 300 kmh while another travels due south at 300 kmh. Are their speeds the same ? are their velocity the same ? Explain Their speeds are the same. However their velocity is not the same because of the different directions they are taking. (3) Can an object reverse its direction of travel while maintaining a constant acceleration ? if so give an example. If not provide an explanation Yes because acceleration is occurring. (4)A ball is tossed up with enough speed straight up so that it is in the air for several seconds . What is the velocity of the ball when it reaches its highest point ? O What is its velocity 1 sec before it reaches its highest point? What is the change in velocity during this 1 sec interval? What is the change in velocity during the 2 sec interval.? What is the acceleration of the ball during any of theses time intervals and at the moment the ball has 0 velocity ? 9.81 (5)A car takes 10 sec from v=0 to v= 25 at constant acceleration . if you wish to find the distance what value of acceleration should you use ? Vf= vi + at 25= 0 +10a 25/10= 2.5 a = 2.5 (6) gravity on the moon is is only 1/6 as strong a gravity on the earth. What is the weight of a 10kg object on the moon and on the earth? What is its mass on each ? 10 x 9.81= 98.1 which is on earth 98.1 x 1/6 = 16.35 which is on the moon (7)Free fall is the motion in which gravity is the only force acting Is a skydiver who has reached terminal speed in free fall? Is a satellite above the atmosphere that circles earth in free fall? The skydiver is not in free fall as he has a reaction force acting on him as well as gravity The satellite is in freefall as it has only gravity working on it . (8) How much force acts on a tossed coin when it is half way to its max height ? how much force acts on it when it reaches its peack ? (9) If a mack truck( m) and Honda civic (2M) have a head ib collision upon which vehicle is the impact force greater? Which vehicle experiences the greater deceleration ? The force of impact is equal and opposite on both. The one with the smaller mass goes through the greater deacceleration . sorry there is a quite a few of them . i could not answear a few of them . please help me with those and please cheack if the ones i did is correct ! thanks !
 Dec 3rd 2012, 03:29 PM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,320 You've done pretty well on these, and I would think that the few you left unanswered you could probably get as well: 3) Give an example of an object undergoing constant acceleration that reverses course - you have a perfect example given in question 4. 4) The velocity 1 second before reaching the highest point: equal in magnitude and opposite in direction from a ball that falls for 1 second with zero initial velocity - you can use v= gt. 8) You can probably answer this already - the force due to gravity is constant.
 Dec 3rd 2012, 04:00 PM #3 Junior Member   Join Date: Dec 2012 Posts: 7 hey thanks man so the ones that i have answered are correct i assume ?
Dec 3rd 2012, 04:13 PM   #4
Physics Team

Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,320
 Originally Posted by Tyson hey thanks man so the ones that i have answered are correct i assume ?
Yep - well done!

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