PHYS 1401 College Physics I CRN 55178 HOMEWORK PROBLEMS Khalid Bukhari HW 2 Chapter 2 MOTION IN ONE DIMENSION PART A Hand in your answers in class on scantron on Wednesday 19 September 2010 1 An arrow is shot straight up in the air at an initial speed of 15 0 m s After how much time is the arrow heading downward at a speed of 8 00 m s a 0 714 s b 1 24 s c 1 87 s d 2 35 s e 3 22 s Dt v f v0 8 00 m s 15 0 m s Dv 2 35 s a g 9 80 m s2 2 A cannon shell is fired straight up in the air at an initial speed of 225 m s After how much time is the shell at a height of 6 20 X 102 m and heading down a 2 96 s b 17 3 s c 25 4 s d 33 6 s e 43 0 s Dy v0 t 1 2 gt 2 1 9 80 m s 2 t 2 2 6 20 102 m 225 m s t 4 90 m s2 t 2 225 m s t 6 20 10 2 m 0 2 t 225 m s 225 m s 4 4 90 m s 2 2 4 90 m s2 6 20 10 2 m with solutions of t 43 0 s and t 2 94 s The projectile is at a height of 6 20 102 m and coming downward at the largest of these two elapsed times so the correct choice is seen to be e 3 When applying the equations of kinematics for an object moving in one dimension which of the following statements must be true a The velocity of the object must remain constant b The acceleration of the object must remain constant c The velocity of the object must increase with time d The position of the object must increase with time e The velocity of the object must always be in the same direction as its acceleration 4 A juggler throws a bowling pin straight up in the air After the pin leaves his hand and while it is in the air which statement is true a The velocity of the pin is always in the same direction as its acceleration b The velocity of the pin is never in the same direction as its acceleration c The acceleration of the pin is zero d The velocity of the pin is opposite its acceleration on the way up e The velocity of the pin is in the same direction as its acceleration on the way up 5 A racing car starts from rest and reaches a final speed v in a time t If the acceleration of the car is constant during this time which of the following statements must be true a The car travels a distance vt b The average speed of the car is v 2 c The acceleration of the car is v t d The velocity of the car remains constant e None of these 1 PHYS 1401 College Physics I CRN 55178 Khalid Bukhari HW 2 6 A pebble is dropped from rest from the top of a tall cliff and falls 4 9 m after 1 0 s has elapsed How much farther does it drop in the next 2 0 seconds a 9 8 m b 19 6 m c 39 m d 44 m e 27 m 1 1 y3 v0 t at 2 0 9 8 m s2 2 2 3 0 s 2 44 m Dy y3 y1 44 m 4 9 m 39 m 7 An object moves along the x axis its position measured at each instant of time The data are organized into an accurate graph of x vs t Which of the following quantities cannot be obtained from this graph a the velocity at any instant b the acceleration at any instant c the displacement during some time interval d the average velocity during some time interval e the speed of the particle at any instant 8 People become uncomfortable in an elevator if it accelerates from rest at a rate such that it attains a speed of about 6 m s after descending ten stories about 30 m What is the approximate magnitude of its acceleration Choose the closest answer a 10 m s2 b 0 3 m s2 c 0 6 m s2 d 1 m s2 e 0 8 m s2 2 v2 v02 6 m s 0 0 6 m s2 a 2 Dy 2 30 m 9 Races are timed to an accuracy of 1 1 000 of a second What distance could a person rollerblading at a speed of 8 5 m s travel in that period of time a 85 mm b 85 cm c 8 5 m d 8 5 mm e 8 5 km Dx v Dt 8 5 m s 1 0 10 3 s 8 5 10 3 m 8 5 mm 10 A student at the top of a building throws a red ball upward with speed v0 and then throws a blue ball downward with the same initial speed v0 Immediately before the two balls reach the ground which of the following statements are true Choose all correct statements neglect air friction a The speed of the red ball is less than that of the blue ball b The speed of the red ball is greater than that of the blue ball c Their velocities are equal d The speed of each ball is greater than v0 e The acceleration of the blue ball is greater than that of the red ball 11 A rock is thrown downward from the top of a 40 0 m tower with an initial speed of 12 m s Assuming negligible air resistance what is the speed of the rock just before hitting the ground a 28 m s b 30 m s c 56 m s d 784 m s e More information is needed v v02 2a Dy v02 2 g h 12 2 m s 2 9 8 m s2 40 0 m 30 m s 12 A ball is thrown straight up in the air For which situation are both the instantaneous velocity and the acceleration zero a on the way up b at the top of the flight path c on the way down d halfway up and halfway down e none of these 2 PHYS 1401 College Physics I CRN 55178 Khalid Bukhari HW 2 13 If the velocity of a particle is nonzero can the particle s acceleration be zero a yes b No 14 If the velocity of a particle is zero can the particle s acceleration be zero a yes b No 15 If a car is traveling eastward can its acceleration be westward a yes b No 16 Can the equations of kinematics be used in a situation where the acceleration varies with time a yes b No 17 Can the instantaneous velocity of an object at an instant of …