Problem Solving Sample Problem 1 Dave decided to go to the grocery. To move the car, he placed his foot on the gas pedal accelerating the car at 2.5m/s? A) What will be his velocity after 10s B) and how far did he travel? Solution: Given: vi = 0m/s a = 2.5m/$2 1 = 10s Formulas to use: a) vr = vit at vy = 0m/s + (2.5m/s2) (10s) v1 = 25m/s b ) d = vit+ = at2 d = (0m/s)(10s) + = (2.5m/s2)(10s)2 1 (250m) d = 0m +7 d = 125 m Practice Problem 1 While riding a bike at a speed of 15m/s, you saw that the traffic light turned red so you gently press the brakes covering a distance of 80m and then stopped. What is your acceleration?Problem Solving Sample Problem 1 Sample Problem 2 Rian is driving at a constant A coin was dropped from a cliff velocity of 5m/s. She hit the gas that hit the ground after 20s. The pedal that increased her velocity acceleration due to gravity is thrice in 10 seconds. What is her 9.8m/s2. Calculate for the final acceleration? velocity of the rock. Solution: Solution: Given: vi = 5m/s v1= 5x3 = 15m/s t Given: vi = 0m/s2 = because it = 10s started from rest Formula: a = 9.8m/$2 1 = 20s Uf - Vi Formula: a = from a = v1 - vi 15m/s - 5m/s to v t a= 10s = vit at a = 1m/s2 v, = 0m/s + 9m/s2(20s) v = 196 m/s Practice Problem 1 Practice Problem 2 A downhill skier reaches the A bowling ball rolled down the steepest part of the trail. His lane in 3s the ball traveled at a speed increased from 12m/s to constant acceleration of 2.4m/s 28m/s in 5s. What is the and travelled at a speed of acceleration. 8.2m/s as it reached the pins. How fast was the ball traveling when it left the player's hands?Problem Solving Sample Problem 1 Sample Problem 2 (relative velocity) Samantha drove 120km for 5 hrs. Barry stood in a moving 40meters What is her speed? moving sidewalk that moves 1.5m/s. Find A) how long it will take for him to Solution: reach the end of the side walk. B) How long it will take if he walked 1.7m/s to Given: d = 120km t = 5hrs reach the end in the same direction. d 120km S= -= 24km/hr 5 hrs Solution A) Given: d = 40m v = 1.5m/s d 40m 1 = 1.5m/s = 26.67s B) Given: d = 40m v = 1.5m/s Velocity of Barry = 1.7m/s 40m 1 = 1. 7m/s + 1.5m/s = 12.5s Practice Problem 1 Practice Problem 2 Find Marlyn's displacement in km if her How long will it take a passenger average velocity is 2.3m/s for 1,550 s. walking at 1.2m/s on a moving side walk with a velocity of 2.5m/s and a distance of 50m if he is moving in an opposite direction?Problem Solving Sample Problem1 A ball is dropped from rest on a cliff. a) What is the speed of the ball after 15 seconds? b) How far did it travel? c) What is the displacement of the ball? Solution: Given: Find V. = 0 1 = 15s a = -9.8m/s2 Formula: a) note that speed is always positive. If you get a negative answer just change the sign. v1 = v,+ gt v/ = (0m/s) + (-9.8m/s') (15s) v1 = 147m/s b and c) d = vitt=gt? d = (15s) +5 (-9.8m)(15s) d = -1102.5m displacement if we'retalking about distance d = 1102.5m distance is positive Practice Problem1 A ball is thrown downward at an initial speed of 21.5m/s from the edge of the building. A) find the speed and velocity after 10s. b) how far did it travel and its displacement