SAT物理练习题1
Question 1:
An object of mass m moving with a velocity v collides with another object of mass 2m. The two objects stick together and they collide with a third object of mass 3m. After the second collision the three objects move together at the same speed. What is the velocity of the three objects after the second collision?
v/12
v/6
v/3
v/2
v
Question 2:
An electric motor accelerates its rotation with a constant angular acceleration of 2 rad/s2 until it reaches a frequency of f = 10/¶ Hz. If the motor starts from rest, how long does it take to reach frequency f?
6s
10s
¶s
12s
15s
Question 3:
Two satellites orbit the earth at radii r1 and r1. What is the ratio of the velocities of the two satellites?
Question 4:
250J of heat are added to a gas in a cylindrical container and then the gas does 120J of work on the top and bottom walls of the cylinder. What is the change in internal energy for the gas?
0J
120J
130J
250J
-120J
Question 5:
Three point charges of charge +Q are placed as shown above. At what point will a negative charge experience a force toward the bottom of the page?
A
B
C
D
E
Question 6:
Resistor R1 = 5Ω and resistor R2 = 10Ω are connected in series to a voltage source E = 60V. What is the ratio between the power dissipation in R2 and the power dissipation in R1?
1
2
3
4
5
Question 7:
Resistor R1 = 4Ω and resistor R2 = 6Ω are connected in series. If the tolerance of R1 is 1% and the tolerance of R2 is 2%, what is the tolerance of the equivalent resistor R?
.8%
1%
1.6%
2%
3%
参考答案与解析参见下一页
Question 1 solution:
According to the law of conservation of momentum,
mv = (m + 2m)v1 and,
(m + 2m)v1 = (m + 2m + 3m)v2, where v1 and v2 are the speed after the first and after the second collision.
In conclusion, mv = 6mv2 and v2 = v/6.
Question 2 solution:
t = ω / ε = 2πf / ε
where ω is the angular speed and ε is the angular acceleration.
t = 2π(10/π) / 2
t = 10s.
Question 3 solution:
We equate the formulas for gravitational force and centripetal force:
mv2/r = GmM/r2
r = radius of the orbit;
m = mass of satellite;
M = mass of planet;
v = speed of satellite;
v12 = GM/r1
v22 = GM/r2
Question 4 solution:
According to the First Law of Thermodynamics, the change in internal energy is equal to the change in heat plus the work done on the system.
ΔU = ΔQ + ΔW = 250J - 120J = 130J.
Question 5 solution:
A and D are the only points that have the horizontal component of the force equal to zero.
A negative charge experiences a force toward the bottom of the page in point A and towards the top of the page in point B.
(a) is the correct answer.
Question 6 solution:
P2 = R2I2
P1 = R1I2
We divide the 2 equations and,
P2/P1 = R2/R1
P2/P1 = 100/50
P2/P1 = 2
Question 7 solution:
R1(1 + t1) + R2(1 + t2) = R(1 + t),
We also know that R1 + R2 = R.
We substract the second equation from the first equation:
R1t1 + R2t2 = Rt,
t = (R1t1 + R2t2)/R
t = (4·1% + 6·2%)/10
t = 1.6% is the tolerance of the series resistor combination.