SAT物理练习题1.

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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%

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• 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.

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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%

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