1. / Linear momentum is the ______.
/ a. / product of the mass and velocity of a moving object
/ b. / quantity of motion used with objects rotating about a fixed axis
/ c. / average force and the time interval over which it acts
/ d. / angular momentum and torque
Hint
2. / In Figure 9-4b, in which position does the diver have the largest moment of inertia?
/ a. / The second
/ b. / The third
/ c. / The fourth
/ d. / The last
Hint
3. / The impulse-momentum theorem states that ______.
/ a. / the impulse on an object is equal to the change in momentum it causes
/ b. / the force on a moving object is equal to the magnitude of the impulse
/ c. / the impulse on an object is greater than the change in momentum it causes
/ d. / the impulse on an object is less than the change in momentum it causes
Hint
4. / The product of the average force and the time interval over which it acts is the ______.
/ a. / impulse
/ b. / velocity
/ c. / acceleration
/ d. / linear momentum
5. / Which of the following is the equation for impulse-momentum?
/ a. / FΔt = mΔv
/ b. / p = mv
/ c. / F = ma
/ d. / g = F/m
Hint
6. / FΔt = mΔv is the equation for ______.
/ a. / impulse-momentum
/ b. / linear momentum
/ c. / angular momentum
/ d. / net force
Hint
7. / Which one of the changes to the situation in Figure 9-2 listed below would require the airbag to exert a larger average force on the passenger?
/ a. / The time required to stop the passenger is lengthened.
/ b. / The passenger's weight is decreased.
/ c. / The initial speed of the passenger is decreased.
/ d. / The time required to stop the passenger is shortened.
Hint
8. / The product of mass and velocity of a moving object is defined as its ______.
/ a. / linear momentum
/ b. / impulse
/ c. / net force
/ d. / normal force
Hint
9. / The impulse is the product of the ______.
/ a. / average force and the time interval over which it acts
/ b. / mass and velocity of a moving object
/ c. / average force and the distance the object travels
/ d. / angular momentum and torque
Hint
10. / A constant force of 4.5 N acts on a 7.2-kg object for 10.0 s. What is the change in the object's velocity?
/ a. / 6.3 m/s
/ b. / 3.2 m/s
/ c. / 1.2 m/s
/ d. / 4.33 m/s
Hint
11. / Your sister's mass is 43.5 kg, and she is riding her 8.00-kg bicycle. What is the combined momentum of your sister and her bike if they are going 2.40 m/s?
/ a. / 85 kg·m/s2
/ b. / 124 kg·m/s2
/ c. / 104 kg·m/s
/ d. / 124 kg·m/s
Hint
12. / Small rockets are used to make tiny adjustments in the speed of satellites. One such rocket has a thrust of 50.0 N. If it is fired to change the velocity of a 75,000-kg spacecraft by 45 cm/s, how long should it be fired?
/ a. / 18.8 min
/ b. / 9.4 min
/ c. / 22 min
/ d. / 11 min
Hint
13. / If an air bag such as the one shown in Figure 9-2 changes a 6.0×101 kg person's speed from 40.0 m/s to 0.0 m/s, what impulse must act on the person?
/ a. / You cannot solve this problem without knowing the time it takes to stop the person.
/ b. / 2400 kg m/s
/ c. / 1.5 kg m/s
/ d. / 0.67 kg m/s
Hint
14. / The velocity of a 975-kg car is changed from 12.0 m/s to 27.0 m/s in 15.0 s by an external, constant force. What is the resulting change in momentum of the car?
/ a. / 1.46×104 kg[dot]m/s
/ b. / 9.75×102 kg[dot]m/s
/ c. / 2.19×105 kg[dot]m/s
/ d. / 7.22×104 kg[dot]m/s
Hint
15. / In Figure 9-4b, in which position does the diver have the smallest moment of inertia?
/ a. / The first
/ b. / The second
/ c. / The fourth
/ d. / The last
Hint
16. / The velocity of a 975-kg car is changed from 12.0 m/s to 27.0 m/s in 15.0 s by an external, constant force. What is the magnitude of the force?
/ a. / 9.75×102 N
/ b. / 1.46×104 N
/ c. / 9.75×103 N
/ d. / 975 kg·m/s
Hint
17. / A 930-kg car traveling 56 km/h comes to a complete stop in 2.0 s. What is the force exerted on the car during this stop?
/ a. / -7.2×103 N
/ b. / 7.2×103 N
/ c. / -2.5×104 N
/ d. / 2.5×104 N
- Hint
Microengines
Microengines are the size of a sand grain but with the power of a horse. Well, not exactly. Though these minature engines etched into silicon do produce horsepower, it is as miniscule as their size.
Figure 1 Microtransmission driving a rack and pinion unit to deflect an out-of-plane mirror.A transmission is a type of machine that uses a set of gears to transmit the input force of the engine to an output force on an object.
Micromachines
To increase the output force of a microengine, one needs to devise a micromachine. Researchers at Sandia National Laboratories have done just that. They have produced a miniature set of gears, a transmission of sorts, that will increase the force a microengine can deliver.
Figure 2 Close up shot of the micromachine. The width of the picture represents 200 µm. How it Works
Figure 2 is an up-close shot of the machine. The microengine is at the top and it will turn the little gear wheel, A. Through a series of other gears, the pinion B (small gear wheel) will turn. The pinion drives the rack C. Notice on Figure 1 that the rack will push or pull on the mirror. What is the ideal mechanical advantage of the micromachine in Figure 2? What is the size of the mirror in Figure 1?