(a) Calculate the force needed to bring a 800 kg car to rest from a speed of 95.

Question

(a) Calculate the force needed to bring a 800 kg car to rest from a speed of 95.0 km/h in a distance of 110 m (a fairly typical distance for a nonpanic stop). Answers In terms of N

(b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. Calculate the force exerted on the car and compare it with the force found in part (a), i.e. find the ratio of the force in part(b) to the force in part(a). Answers In terms of (force in part (b) / force in part (a))

Explanation / Answer

a) v^2 = u^2 + 2*a*S

=> 0 = (95*0.277)^2 + 2*(a)*110

=> -692.47 =220*a

=> a = -3.14 m/s^2

=> force needed F = 800*3.14 = 2512 N

b) v^2 = u^2 + 2*a*S

=> 0 = (95*0.277)^2 + 2*(a)*2

=> -692.47 =4*a

=> a = -173.11 m/s^2

=> force exerted on car F = 800*173.11 = 138494 N

Fb/Fa = 138494/2512 = 55.13

force exerted in part b is higher than part a .

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