Name ______Chapter 9 Practice test

1. A see-saw (teeter-totter) is 4 meters long and has a mass of 15 kg

a. A student pushes down .25 meters away from the pivot (which is right in the center of the see-saw) with 4 N of force. How much torque is created?

b. If the student did not want to push any harder, but wanted to create more torque, where should they push? At what angle to the see-saw should they push? What is the maximum torque they could create with a force of 4 Newtons?

c. If the student again pushes with 4 N of force, this time on one end but at an angle of 70 degrees to the see-saw what torque do they create?

d. A different student pushes with 10 Newtons of force perpendicular to the see-saw and creates 7Nm of torque. How far from the pivot did they push?

e. How hard would a student have to push, perpendicularly on the very end, to create 6Nm of torque?

f. If two students stood on opposite ends of the see-saw and both students push down just hard enough to keep the see-saw from moving either direction, what would the sum of their two torques be? If they are both pushing down, is it possible for the two torques to ever cancel out? How?

2. A 15000 kg bridge is 60. meters long and is supported by two pillars right on the very ends. A 3500 kg car is parked 20 meters from the left end. Find the force both pillars are providing.

3. Two masses are placed on a meter stick. 50 g is placed at the 30 cm mark, and 500 g is placed at the 95 cm mark. The meter stick has a mass of 100 g. Where should the pivot be placed to balance the meter stick?

4. A 20 kg sign is hanging from the very end of a 85 N beam on the side of a building. The beam is 1.4 meters long and is supported with a cable that makes at 65 degree angle with the beam and connects at the very end. Find the tension in the cable.

Bonus: Does the hinge exert any forces? If so calculate them.

5. A bowler rolls a 7 kg bowling ball that has a .15 m radius down the lane.

a. Which rotational inertia equation would you choose to use to describe the rotational inertia of the bowling ball?

b. What is the bowling ball’s rotational inertia?

c. If the bowlers wants to spin the ball sideways with an angular acceleration 13 rad/s/s, how much torque must she supply?

d. How much force will she need to supply to the outer edge of the bowling ball to create that much torque?

6. A soccer player swings his leg (length 1.2 m; mass 18 kg) to kick a ball

Which rotational inertia equation would you choose to use to describe his leg?

What is his legs’s rotational inertia?

If his hip muscles are capable of providing 60 Nm of torque, at what angular acceleration can he swing his leg?

7. A torque of 3.3 Nm causes a 0.68 kg hula hoop to accelerate at 15 rad/s/s.

a. What is the rotational inertia of the hula hoop?

b. Which rotational inertia equation best matches a hula hoop?

c. Using that equation, what is the radius of the hula hoop?