YIJC Topic 4_MCQ_Set A and B

04 Energy and Fields 1 | Yishun Innova Junior College Practice A (10 MCQs) 1 An old -fashioned 60 W lamp converts 95% of its energy supply into heat. A 4.0 W modern lamp has the same power output of light as the old-fashioned lamp. What is the efficiency of the modern lamp? A 5.0% B 6.7% C 75% D 95% [Prelim2020/ASRJC/1/10] 2 A car with a power output of 90 kW can travel at a maximum speed of 55 m s –1 along a straight horizontal road. The drag force on the car is directly proportional to the square of its speed. What is the maximum speed of the car, if the power output of the car is reduced to 50 kW while travelling on the same road? A 131 m s− B 141 m s− C 145 m s− D 167 m s− [Prelim2020/JPJC/1/6] 3 An object of mass 1.5 kg slides down a rough plane inclined at 10° above the horizontal, as shown. The object has an initial speed of 5.0 m s–1 at point O, and comes to rest at point P after sliding 85 cm down the slope. What is the work done by the frictional force on the object between points O and P? A – 31 J B – 21 J C 21 J D 31 J [Prelim2020/JPJC/1/7] 4 The variation with force F of the length x of a spring is shown below. The tension in the 10° 85 cm 5.0 m s–1 O P

04 Energy and Fields 2 | Yishun Innova Junior College spring is increased from F1 to F2, causing the length to increase from x1 to x2. The work done in stretching the spring from x1 to x2 is given by the area A LMS B MNRS C LMP D MNQP [Prelim2020/TMJC/1/8] 5 Two springs labelled spring 1 and spring 2 are supporting a load of 80 N as shown. Spring 1 has an elastic constant k1 = 4 kN m–1 and spring 2 has an elastic constant k2 = 2 kN m–1. What is the ratio elastic potential energy stored in the spring 1 ? elastic potential energy stored in the spring 2 A 4:1 B 2:1 C 1:4 D 1:2 M F / N x / m x2 x1 N Q 0 P F2 F1 R S spring 1 spring 2

04 Energy and Fields 3 | Yishun Innova Junior College [Prelim2020/TJC/1/8] 6 The diagram shows a lift system in which the elevator (mass m1) is partly counterbalanced by a heavy weight (mass m2). At what rate does the motor provide energy to the system when the elevator is rising at a steady speed v? ( g = acceleration of free fall ) A 1 2 m1v 2 B 1 2 m1 - m2( )v 2 C m1gv D m1 - m2( ) gv [Prelim2020/RVHS/1/7]

04 Energy and Fields 4 | Yishun Innova Junior College 7 A ball rolls down the circularly curved track shown below. Which of the following correctly describes its speed, acceleration along the slope and kinetic energy? speed acceleration kinetic energy A increases increases increases B decreases decreases decreases C increases decreases increases D increases constant increases [Prelim2020/NYJC/1/9] 8