Physics Help, tell me what i did wrong....please?

Question

Sample Calculation: Trial 1

Weight= 176 lbs. 1 pound= 2.21 Kg
176/2.21= 79.6 Kg
79.6Kg * 9.81= 781.2 N (Force)

Pet= KeB
Mgh=.5mv^2

79.6 (9.81) (2.87)= .5 (80) v^2
2241.1= 40v^2
2241.1/40= v^2
V^2= 56.02
V= 7.484 m/s

7.484= 0 + A(14.8)
14.8A= 7.484
A= 0.51 m/s
Vf^2= Vi^2 + 2ad
7.484^2= 0+2(0.51)D
56.01= 1.02d
D= 54.9 m

W= F * D
W= 781.2 * 54.9
W= 42,887.88 J
W= 42.8 KJ
Power= work/t
Power= 42887.88 J/ 14.8s
Power= 2897 W

when i try to check my answers using P=F*V P= 781.2 * 7.484 i dont get 2897, i get 5000

even when i changed its to 388 i got different answers

this is not an actual problem. it is a lab in which we are trying to find power. we are given time of 14.8 a height of 2.87, my mass which is 80kg.

Answer 1

I tried to desipher the problem but could't figure it out.

It doesn't look like the velocity is constant. F*V is instantaneous power.

BTW: 2.21lb=1kg although you did the actual calculation correctly

j

Answer 2

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Answer 3

If 1lb is 2.21kg (sorry but I'm not double checking it for you), 176lb should be 176*2.21=388.96kg.