Which requires more work, lifting a 2 kg rock to a height of 9 m without accelerating, or accelerating the same rock horizontally from rest to a speed of 14 m/s?
Work to lift rock?
J
Work to accelerate rock?
J
2007-02-05 17:20:02 · 3 answers · asked by bibun 2 in Science & Mathematics ➔ Physics
To lift: You are working against the acceleration due to gravity.
F = ma = mg
W = Fd = mgd = (2 kg)(9.8 m/s/s)(9 m) =176.4 J
To accelerate horizontally, unless there is a way I'm not seeing, you are missing a time factor. You have the final velocity, but need t to know the acceleration in the problem. (mass)(velocity)(kg) does not give joules, which is kilogram-meters squared per second squared.
a = v/t
W = Fd = mad
W =m(v/t)d
W = Fd = (2 kg)(14 m/s)/t(9 kg) = 252/t J
2007-02-05 18:24:54 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Without doing any math or serious thinking, I'd have to say horizontally. 14 m/sec is pretty fast, so would take more energy to achieve than simply lifting the rock.
2007-02-06 01:26:49 · answer #2 · answered by alisongiggles 6 · 0⤊ 0⤋
W=fxd
W=20N x 9m = 180J
W=fxd=mxaxd= 2kg x 14m/s x 9m =253J
Accelerating the rock.
2007-02-06 01:30:18 · answer #3 · answered by Cat 3 · 0⤊ 0⤋