Question

10. How much work is done when a ping pong ball of mass .40 kg speeds up from 6 m/s to 10 m/s in 45 seconds and travels 14 km?

a) 5 x 10-2 J b) 5 x 102 J c) 5 x 10-4 J d) 5 x 104 J

11. Convert 4π/3 radians to degrees. ___________________________.

12. A physics textbook is dropped from 20 m and has a mass of 14 kg. What is its kinetic energy 5/9 of the way down?

a) 2776 J b) 1666 J c) 1388 J d) 1524 J

13. If you lift a 500 N weight 3 m from the ground during a period of 4 seconds, how much work did you do?

a) 1500 J b) 1300 W c) 1500 W d) 1300 J

14. Convert 78 degrees to radians. ____________________________________.

15. Energy cannot be ___________________ or _______________________.

a) transferred, lost b) created, destroyed c) conserved, transferred d) lost, gained

Answer 1

10) increase in kinetic energy = 0.5*0.4*(10²-6²)=12.8 Joules

acceleration = (10-6)/45=0.089 m/s²

inertia force on ball=0.4*0.089=0.0355 N

work done by inertial force=0.0355*14000=497.7 Joules

Total work done=12.8+497.7=510.6 Joules

Correct option is (b)

11) We know that radians = 180^o

4/3 radians= (4/3)*180=240^o

12)inital potential energy = 14*9.8*20=2744 joules

potential energy of book when it is 5/9 of the way down = 14*9.8*(4/9)*20=1219.56 Joules

Kinetic energy of book = 2744-1219.56=1524.4 Joules

Corrcet option is (d)

13)Work done = increase in potential energy of weight = 500*3=1500 Joules

14) we know that 180^o = radians

78^o = (/180)*78=1.36 radians

15) Anser is destroyed. Energy cannot be destroyed. It can be just transformed/transferred/lost/gained