Squaring Equation 2.7 gives an expression for v^2. Equation 2.11 also gives an e

Question

Squaring Equation 2.7 gives an expression for v^2. Equation 2.11 also gives an expression for v^2. Equate the two expressions, and show that the resulting equation reduces to Equation 2.10. On packed snow, computerized antilock brakes can reduce a car's stopping distance by 55%. By what percentage is the stopping time reduced? A particle leaves its initial position x_0 at time t = 0, moving in the positive x-direction with speed v_0 but undergoing acceleration of magnitude a in the negative x-direction. Find expressions for (a) the time when it returns to x_0 and (b) its speed when it passes that point. A hockey puck moving at 32 m/s slams through a wall of snow 35 cm thick. It emerges moving at 18 m/s. Assuming constant acceleration, find (a) the time the puck spends in the snow and (b) the thickness of a snow wall that would stop the puck entirely.

Explanation / Answer

55) By third equation of motion,

v^2 = u^2 +2as

a = (18^2 - 32^2) / (2*0.35)

= - 1000 m/s^2

t = (18-32)/-1000

= 0.014 s answer

B) s = u^2 /2a

= -32^2 /(2*-1000)

= 0.512 m

= 51.2 cm answer

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