|
Kẻ mạnh không phải lúc nào cũng là kẻ chiến thắng. Kẻ chiến thắng mới chính là kẻ mạnh
<!--
1. 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
The change in the obejct's velocity is 6.3 m/s.
2. The quantity of momentum used with objects rotating about a fixed axis is called __________.
a. angular momentum
b. torque
c. uniform circular motion
d. centripetal acceleration
Angular momentum is measured in kg&#middot;m2/s.
3. Which of the following is the equation for impulse-momentum?
a. FΔt = mΔv
b. p = mv
c. F = ma
d. g = F/m
FΔt = mΔv is the equation for impulse-momentum.
4. 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
The smaller the moment of inertia, the easier it is for an object to spin.
5. FΔt = mΔv is the equation for __________.
a. impulse-momentum
b. linear momentum
c. angular momentum
d. net force
The momentum of an object is equal to the mass of the object multiplied by the object's velocity.
6. 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
The magnitude of the force can be found by dividing the change in momentum by the time interval. The magnitude of the force is 9.75×102 N.
7. 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
The impulse on an object is equal to its change in momentum.
8. 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
The impulse on a object is equal to the change in momentum of the object.
9. 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
Convert cm/s to m/s. Multiply change in velocity by the mass, then divide by the force applied to find the time interval. The rocket should be fired for 11 mintues.
10. 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
Since F = pf - pi/Δt, F = -7.2×103 N. Remember to convert km/h to m/s before solving for pi.
11. 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.
The average force required is equal to the change in momentum of the object, divided by the time it has to act on that object.
12. 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
The impulse-momentum theorem is represented by the following equation: FΔt = Pf - Pi.
13. 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
Momentum is measured in kg&#middot;m/s.
14. 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
7If the force on an object is constant, the impulse is the product of the force and the time interval over which it acts.
15. 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
Momentum is measured in kg&#middot;m/s.
16. 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
The larger the moment of inertia, the harder it is for an object to spin.
17. 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
Since momentum is equal to mass times velocity, the combined momentum is the product of the total mass of the girl and the bike, multiplied by their velocity, 2.40 m/s. The combined momentum of your sister and her bike is 124 kg·m/s.
18. 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
The change in momentum of the car can be found by multiplying the mass times the change in velocity. The resulting change in the momentum of the car is 1.46×104 kg[dot]m/s.
aaacaabadadaaaadda
-->
| 