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Sample Questions Which of the following are proper units for acceleration? a) N b) Kg m/s2 c) N/m2 d) m/s2 e) m2/s The speedometer of a car indicates a constant speed. Can the car be accelerating? a) Yes b) No A body falls from rest. If air resistance is negligible, what is the velocity of the body after falling for 10 seconds? a) 10 m/s b) 9.8 m/s c) 98 m/s d) 0.98 m/s e) 490 m/s A rifle is fired straight downward from a high-altitude balloon. If the bullet leaves the barrel at 100 m/s, then its speed one second later (neglecting air resistance) will be about a) 9.8 m/s b) 98 m/s c) 104.9 m/s d) 109.8 m/s What is the acceleration of a rock at the top of its trajectory when thrown straight up? a) 0 m/s2 b) 4.9 m/s2 c) 9.8 m/s2 d) 4.9 m e) 9.8 m What is the velocity of a rock at the top of its trajectory when thrown straight up? a) 0 m/s b) 4.9 m/s c) 9.8 m/s d) 490 m e) 9.8 m Which of the following balls would hit the ground first if they were all dropped at the same time from the same height (10 ft) in a vacuum? a) 15-lb feather ball b) 20-lb wood ball c) 10-lb lead ball d) They all it at the same time The two measurements necessary for calculating acceleration are a) Velocity and Time b) Distance and Time c) Distance and Acceleration d) Velocity and Distance What is the acceleration of a vehicle that changes is velocity from 10m/s to a dead stop in 10 seconds? a) -1 m/s2 b) -100 m/s2 c) -0.01 m/s2 d) 0 m/s2 You throw a ball straight up. On the way up… a) the velocity and acceleration both have an upward direction b) the velocity has an upward direction and the acceleration has a downward direction c) the velocity and acceleration both have an downward direction d) the velocity has an downward direction and the acceleration has a upward direction Attendance check – write your name and the answer to this question on a piece of paper and hand it in What is the instantaneous velocity of a freely falling object 10 s after it is released from a position of rest? v = at v = ?? a = 9.8 m/s2 t = 10 s v = (9.8 m/s2)(10 s) = 98 m/s How far will it fall during this time? d = do + vot + ½at2 d = ?? do = 0 vo = 0 a = 9.8 m/s2 t = 10 s So, d = ½(9.8 m/s2)(10 s)2 = 490 m What is the average velocity during this 10-s interval? vavg = (vf – vo)/2 vo = 0 m/s vf = 98 m/s vavg = (98 m/s – 0 m/s)/2 = 49 m/s What is the acceleration of a vehicle that changes its velocity from 0 m/s to 50 m/s in 10 s? a = (vf – vo)/Dt vo = 0 m/s vf = 50 m/s Dt = 10 s a = (50 m/s – 0 m/s)/(10 s) = 5 m/s2 Surprisingly, very few athletes can jump more than 2 feet (0.6m) straight up. What is the “hang time” for this jump? d = ½at2 gives the time to fall d = 2 ft a = 32 ft/s2 2d 2(2ft) t 2 0.35 s a 32ft/s Total time in the air = 0.7 s An airplane is flying at 350 mph SW while in the jet stream, which is blowing at 100 mph from west to east. What is the speed and direction of the plane with respect to the ground? 100 mph W Add the following forces 30° 60° 50 N 50 N Free Body Diagrams A football is moving upwards towards its peak after having been booted by the punter. A free-body diagram for this situation looks like this: A skydiver is descending with a constant velocity. Consider air resistance. A free-body diagram for this situation looks like this: A car is coasting to the right and slowing down. A free-body diagram for this situation looks like this: