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Dynamics Force Problems Day #1
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Example #1 A 1000kg car is pushed with a force of 300N
What is the acceleration of the car? How long would it take to accelerate to 108 km/h? What force would be required to stop the vehicle in 30m from a speed of 108km/h?
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G: R: F: a Time (v2 = 30 m/s) F (dist = 30 m) m = 1000 kg F = 300 N S: π= βπ£ βπ‘ βπ‘= βπ£ π βπ‘= 30β0 0.3 βπ‘=100π π£ 2 2 = π£ ππ 0= π£ ππ β π£ 1 2 =2ππ β π£ π =π β (30) =π β15π/ π 2 =π πΉ=ππ πΉ=1000 β15 πΉ=β15000 π a) πΉ=ππ πΉ π =π =π 0.3 π/ π 2 =π b) c)
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Example #2 A 70kg person is standing in an elevator. What is the normal force acting on the person if The elevator is at rest The elevator is moving up at 2 m/s The elevator is accelerating downward at a rate of 2 m/s2
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G: R: F: FN (at rest) FN (up at 2 m/s) FN (accel at 2 m/s2) m = 70 kg
b) Since there is no, acceleration there is no net force. Therefore: 686π[π]= πΉ π c) πΉ = πΉ π + πΉ πΊ βππ= πΉ π β πΉ πΊ βππ+ππ= πΉ π m(πβπ)= πΉ π 70 9.8β2 = πΉ π 546π [π]= πΉ π πΉ = πΉ π + πΉ πΊ 0= πΉ π β πΉ πΊ mπ= πΉ π (70)(9.8)= πΉ π 686π[π]= πΉ π * At rest, no net force
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