AP Physics B
C. Solving Word Problems
ex) A car produces a 92 m skid mark with a deceleration of 7.00 m/s^{2}. What speed was the car travelling just before it applied the brakes?
V_{f}^{2} = V_{i}^{2} + 2aΔd 0 = V_{i}^{2} + 2(7.00 m/s^{2})92 m
V_{i}^{2 }= 1288
Δd = 36 m/s
ex) A car accelerates uniformly from rest at a rate of +10 m/s^{2}. How far will the car travel in 4 seconds?
• Step 2  Turn all your information into letters
• Step 3  Substitute and Solve Equation:
Δd = V_{i}t + 1/2aΔt^{2}
= 0 m/s(4 sec)+1/2(10 m/s^{2})(4s)^{2}
Δd = 0 + 5(16)
Δd = 80 m
Ex) If a car traveling 20 mph can stop in about 40 ft. If the same car was traveling twice as fast, how far would it take to stop?
V_{f}^{2} = V_{i}^{2} + 2aΔd
0= V_{i}^{2} + 2aΔd
V_{i}^{2} = 2aΔd
4 times further
160 ft
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