University:
College
Course:
College Physics
Academic year:

2022
Views:

279

Pages:

2
Author:

5CelestialChronicle

Name Class Concept-Development Date Practice Page Friction 1. A crate ﬁlled with delicious junk food rests on a horizontal ﬂoor. Only gravity and the support force of the ﬂoor act on it, as shown by the vectors for weight W and normal force n. a. The net force on the crate is (zero) (greater than zero). b. Evidence for this is no acceleration . 2. A slight pull P is exerted on the crate, not enough to move it. a. The force of friction f acting on the crate is (less than) (equal to) (greater than) P. b. The net force on the crate is (zero) (greater than zero). 3. Pull P is increased until the crate begins to move. It is pulled so that it moves with constant velocity across the ﬂoor. a. Friction f is (less than) (equal to) (greater than) P. b. Constant velocity means acceleration is (zero) (greater than zero). c. The net force on the crate is (less than) (equal to) (greater than) zero. 4. Pull P is further increased and is now greater than friction f. a. The net force on the crate is (less than) (equal to) (greater than) zero. b. The net force acts toward the right, so acceleration acts toward the (left) (right). 5. If the pulling force P is 150 N and the crate doesn’t move, what is the magnitude of f? 150 N 6. If the pulling force P is 200 N and the crate doesn’t move, what is the magnitude of f? 200 N 7. If the force of sliding friction is 250 N, what force is necessary to keep the crate sliding at constant velocity? 250 N 8. If the mass of the crate is 50 kg and sliding friction is 250 N, what is the acceleration of the crate 2 2 2 when the pulling force is 250 N? 0 m/s 300 N? 1 m/s 500 N? 5 m/s Falling and Air Resistance Bronco skydives and parachutes from a stationary helicopter. Various stages of fall are shown in positions (a) through (f). Using Newton’s second law, ﬁnd Bronco’s acceleration at each position (answer in the blanks to the right). You need to know that Bronco’s mass m is 100 kg so his weight is a constant 1000 N. Air resistance R varies with speed and cross-sectional area as shown. 10 m/s2 6 m/s2 0 m/s2 Circle the correct answers. 1. When Bronco’s speed is least, his acceleration is (least) (most). 2. In which position(s) does Bronco experience a downward acceleration? (a) (b) (c) (d) (e) (f) 3. In which position(s) does Bronco experience an upward acceleration? (a) (b) (c) (d) (e) (f) 4. When Bronco experiences an upward acceleration, his velocity is –2 m/s2 Note that we take acceleration down as + here. If chosen as –, then – signs become +. Either way is okay if you’re consistent in any one situation. (still downward) (upward also). 5. In which position(s) is Bronco’s velocity constant? (a) (b) (c) (d) (e) –10 m/s2 (f) 6. In which position(s) does Bronco experience terminal velocity? (a) (b) (c) (d) (e) (f) 7. In which position(s) is terminal velocity greatest? (a) (b) (c) (d) (e) (f) 8. If Bronco were heavier, his terminal velocity would be (greater) (less) (the same). CONCEPTUAL PHYSICS 0 m/s2