Power Knowledge-Based Download PDF

Questions

1. 1.

   A boat moves through water at a constant speed against a resistive drag force that is directly proportional to the square of its speed. By what factor must the propulsion power increase in order to double the speed of the boat?

   • A) 2
   • B) 4
   • C) 6
   • D) 8
2. 2.

   An electric car accelerates along a straight, level road while its motor delivers a constant mechanical power output. Assuming resistive forces are negligible, how do the forward driving force and the acceleration of the car change as its speed increases?

   • A) Both the driving force and the acceleration decrease.
   • B) Both the driving force and the acceleration remain constant.
   • C) The driving force decreases, while the acceleration remains constant.
   • D) The driving force remains constant, while the acceleration decreases.
3. 3.

   A motorized winch pulls a crate horizontally across a floor at a constant speed of 2.5 m/s using a cable inclined at 60° above the horizontal. If the tension in the cable is 400 N, what is the power delivered by the winch to the crate?

   • A) 500 W
   • B) 866 W
   • C) 1000 W
   • D) 200 W
4. 4.

   An object of mass $m$ accelerates from rest along a straight horizontal track under the action of a constant net force. How does the instantaneous power delivered to the object vary with elapsed time $t$?

   • A) It remains constant over time.
   • B) It is inversely proportional to $t$.
   • C) It is directly proportional to $t$.
   • D) It is directly proportional to $t^2$.
5. 5.

   What physical quantity is represented by the gradient of a work versus time graph?

   • A) Force
   • B) Power
   • C) Kinetic energy
   • D) Linear momentum
6. 6.

   Two cranes, P and Q, lift identical containers through the same vertical height at a constant speed. If Crane P completes the lift in 20 s and Crane Q completes the lift in 40 s, which statement correctly compares their work done and average power output?

   • A) Crane P performs twice as much work as Crane Q, but both cranes develop the same average power.
   • B) Both cranes perform the same work, but Crane P develops twice the average power of Crane Q.
   • C) Crane P performs twice as much work and develops twice the average power of Crane Q.
   • D) Both cranes perform the same work, and both cranes develop the same average power.
7. 7.

   An electric motor with an efficiency of 75% performs 54 kJ of useful mechanical work in 45 s. What electrical power input is required to operate the motor?

   • A) 900 W
   • B) 1200 W
   • C) 1600 W
   • D) 2400 W
8. 8.

   A 1200 kg car accelerates uniformly from rest to a speed of 20 m/s along a level track in 8.0 s. Assuming resistive forces are negligible, what is the average power required to produce this acceleration?

   • A) 3.0 kW
   • B) 15 kW
   • C) 30 kW
   • D) 60 kW
9. 9.

   A car travels along a straight, level road at a constant speed of 25 m/s against a total resistive force of 800 N. What mechanical power output must the engine develop to maintain this motion?

   • A) 20 kW
   • B) 32 W
   • C) 825 W
   • D) 200 kW
10. 10.

    An electric motor lifts a load with a weight of 600 N vertically through a height of 12 m at a constant speed in 8.0 s. What is the average power delivered by the motor?

    • A) 900 W
    • B) 7200 W
    • C) 400 W
    • D) 57 600 W