Hi there! Have questions about your homework? At Brainly, there are 60 million students who want to help each other learn. Questions are usually answered in less than 10 minutes. Try it for yourself by posting a question! :D

Hi there! Have questions about your homework? At Brainly, there are 60 million students who want to help each other learn. Questions are usually answered in less than 10 minutes. Try it for yourself by posting a question! :D

(1) A boy weighing 350 N runs up a flight of 30 steps, each 20cm high in 1 minute. Calculate: (a) the work done and (b) the power spent

(2) A truck weighing 1000 kgf changes its speed from 36 km/hr to 72 km/hr in 2 minutes. Calculate: (a) the work done by the engine and (b) its power (g=10m/s²) (3) How much energy is gained by a box of mass 20 kg when a man (a) carrying the box waits for 5 minutes for a bus (b) runs carrying the box with a speed of 3 metre per second to catch the bus?

1: a: given, force = 350 N 1 step = 20 cm therefore 30 such steps will be of = 30 * 20 = 600 cm =6 m time = 1 min = 60 sec work done = Fs = 350 * 6 =2100 J therefore work done = 2100 J ___________________ b: now, power = energy / time power = 2100/60 = 210/6 = 70/2 power = 35 W therefore power spend = 35 W ------------------------------------------------------------------------------------------------------------- 2: given , mass = 1000 kg initial velocity = 36 km/hr = 10 m/s final velocity = 72 km/hr = 20 m/s time = 2 min = 2 * 60 = 120 sec acceleration = 10 m/s² work = F*s therefore s ( distance ) , 2as = v² - u² 2 ( 10 ) ( s ) = 20² - 10² 20 s = 400 - 100 s = 300 / 20 s = 15 m therefore , work = Fs = 1000 * 10 * 15 = 150000 J = 1.5 * 10⁵ J therefore work done = 1.5 * 10⁵ J ____________________ b: now , power = energy / time power = 150000/ 120 power = 1250 W. ------------------------------------------------------------------------------------------------------------ 3: a: no work has been done since the man is waiting he should make some displacement for doing any work therefore the answer is no energy had been transferred by the man . __________ b: mass = 20 kg time = 5 min = 5 * 60 = 300 sec velocity = 3 m/s therefore energy , = 1/2 mv² = 1/2 * 20 * 3² = 10 * 9 = 90 J therefore the energy gained by the box = 90 J ------------------------------------------------------------------------------------------------------------- i hope that this will help u...............................keep smiling friend ^_^

1: a: F = 350 N S = 30 * 20 = 600 cm =6 m work done = Fs = 350 * 6 =2100 J WORK = 2100 J

b: power = energy / time power = 2100/60 = 210/6 = 70/2 power = 35 W

2: mass = 1000 kg initial velocity = 36 km/hr = 10 m/s final velocity = 72 km/hr = 20 m/s time = 2 min = 2 * 60 = 120 sec acceleration = 10 m/s² work = F*s 2as = v² - u² 2 ( 10 ) ( s ) = 20² - 10² 20 s = 400 - 100 s = 300 / 20 s = 15 m work = Fs = 1000 * 10 * 15 = 150000 J = 1.5 * 10⁵ J b: power = energy / time power = 150000/ 120 power = 1250 W. 3: a: no work has been done since the man is waiting he should make some displacement for doing any work therefore the answer is no energy had been transferred by the man . b: mass = 20 kg time = 5 min = 5 * 60 = 300 sec velocity = 3 m/s energy , = 1/2 mv² = 1/2 * 20 * 3² = 10 * 9 = 90 J