Question

16. | Two identical cars, #1 g with 20 m/s and #2 moving with 40 m/s, slam on the brakes at the same time [same braking #1 stops after 3 seconds. #2 still moves after 3 sec with how much of its original momentum? A) 4 D) 1 E) None of these 17 If a car engine e a constant power output for all rpm's (rotational speed [we stay in the same gear all the time The torque would 1. be constant 2. decrease linearly with rpm's. 3. increase linearly with rpm's. . decrease quadratically with rpm's. 5. None of these. 18. A space station (mass 1,000 kg/ initially moving with 10 m/s in the Fires its rockets with a thrust of 1,000 N pushing in the -y direction The magnitude of the final velocity is A) Smaller than the initial speed B) Larger than the initial speed C) The same as the initial speed. D) None of these 9. A solid dise, radius R -2m and moment of inertia 1 -20 kg m is driven by a motor accelerating it from zero to 5 rad/s in 10 seconds. If the disc were made of a lighter material such that it had twice the radius with the same mass - How long would this take to get to 5 rad/s when accelerated by the same motor? a) 10s b) 5s c) 20s d) 40s e) none of these

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Answer 1

16. Impulse on car #1, Fxt = mΔν Fx3= m(v; - v;) Fx3 = m(0-20) Fx3=-20m F= 20m For car #2 Fxt = mΔν Fx3= m(v, – v;) Fx3= m(v; -40) -20m x3m(v; - 40) 3 mv, = 20m initial momentum of the car #2 is 40m and from the above calculation final momentum is 20m. therefore, final momentum is half of the original momentum 17. The relation bwteen the power, RPM, and torque is, - HP 5252 T =- RPM Here, power is constant for RPM's so, the torque would decrease linearly with rpm's