AP Physics B

 

Ever see an object roll UP hill?

 

 

C. Solving Word Problems

 

 

ex) A car produces a 92 m skid mark with a deceleration of 7.00 m/s2. What speed was the car travelling just before it applied the brakes?

 

 

Vi = ?

a = -7.00 m/s2

Vf = 0

Δd = 92 m

 

 

 

 

 

 Vf2 = Vi2 + 2aΔd

 0 = Vi2 + 2(-7.00 m/s2)92 m

 

 

Vi2 = 1288

 

 

Δd = 36 m/s

 

 

ex) A car accelerates uniformly from rest at a rate of +10 m/s2. How far will the car travel in 4 seconds?

 

  

• Step 2 - Turn all your information into letters

 

Vi = 0 (starts from rest)

a = +10 m/s2

t = 4 seconds

d = ?

 

 

• Step 3 - Substitute and Solve Equation:

 

 

 

 Δd = Vit + 1/2aΔt2

 

= 0 m/s(4 sec)+1/2(10 m/s2)(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?

 

 Vf2 = Vi2 + 2aΔd

 

0= Vi2 + 2aΔd

 

 -Vi2  = 2aΔd

 

4 times further

 

160 ft

 

 

 

 

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