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Question

a boy exerts an average force of 65N when he lifts a box 1.2 meters how much work does he do?

(A)0J (B)54J (C)66J (D)78J

how much power is required to do 180J of work in 2.4s?

(A)7.5 W (B) 75W (C)178W (D)430W

Answer 1

Definition of work:  A joule is the amount of work done when a force of one Newton is applied through a distance of one meter.

So, (65 N)(1.2 m) = your answer in joules since a joule is N-m.

Power = Energy/Time, or Power = Work/Time. Because work and energy are measured in joules and time is measured in seconds power is measured in joules per second. One joule per second is defined as one watt.

So, 180 J/ 2.4 s = your answer for power in J/s.

Answer 2

1 joule = Nm

So, when N = 65 and m = 1.2,

joules = 65 * 1.2  = 78 J

Therefore, Answer 1 = 78 joules

power = work done/time

Here, work done is 180J and time is 2.4 seconds,

So, power = 180/2.4 = 75 W

Therefore answer2 = 75 W