Physics 111 SI Worksheet 4 1. A 20 kg box sits on a horizontal surface. The forces required to set it in motion and then to keep it in motion at a constant velocity are 150 N and 120 N, respectively. What are the coefficients of static and kinetic friction? 2. In the apparatus shown, m1=10 kg and the coefficients of static and kinetic friction between m1 and the table are 0.60 and 0.40, respectively. (a) What mass of m2 will set the system in motion? (b) With mass m2 as in part (a), after the system moves, what is the acceleration? 3. A 50-kg gymnast hangs vertically from a pair of parallel rings. (a) If the ropes supporting the rings are attached to the ceiling directly above, what is the tension in each rope? (b) If the ropes are supported so that they make an angle of 45° with the ceiling, what is the tension in each rope? 4. While being loaded from a moving truck, a 10 kg suitcase is placed on a flat ramp inclined at 37°. When released from rest the suitcase accelerates down the ramp at 0.15 m/s2. What is the coefficient of kinetic friction between the suitcase and the ramp? 5. A 23 kg child goes down a straight slide inclined at 38° above horizontal. The child is acted on by his weight, the normal force from the slide, kinetic friction, and a horizontal rope exerting a 30 N force as shown below. How large is the normal force of the slide on the child? 6. A truck of mass 3000 kg tows a 15000 kg car by a chain. If the forward force on the truck by the ground is 3200 N, (a) what is the acceleration of the car? (b) What is the tension in the connecting chain? 7. Sam, whose mass is 75 kg, takes off across level snow on his jet-powered skis. The skis have a thrust of 200 N and a coefficient of kinetic friction on snow of 0.10. Unfortunately, the skis run out of fuel after only 10 s. (a) What is Sam’s top speed? (b) How far has Sam traveled when he finally coasts to a stop?

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