physics ( work, energy and power)
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A crate of mass 80kg sits on the floor. the crate must be brought to the top of a loading dock by sliding it up a ramp 2.5m long, inclined at 30 degrees. the worker, giving no thought to the force of friction, calculates that he can get the crate up the ramp by giving it an initial speed of 5m/s at the bottom and letting it go. unfortunately, friction is negligible, the crate slides up 1.6m on the ramp, stops, and slides back down.
using conservation of energy, show that the initial speed of 5.om/s as calculated by the worker is correct if friction is negligible -
using conservation of energyOriginally posted by starmoonsun:A crate of mass 80kg sits on the floor. the crate must be brought to the top of a loading dock by sliding it up a ramp 2.5m long, inclined at 30 degrees. the worker, giving no thought to the force of friction, calculates that he can get the crate up the ramp by giving it an initial speed of 5m/s at the bottom and letting it go. unfortunately, friction is negligible, the crate slides up 1.6m on the ramp, stops, and slides back down.
using conservation of energy, show that the initial speed of 5.om/s as calculated by the worker is correct if friction is negligible
all KE converts to PE
(1/2)(m)(v^2)=mgh
(1/2)(v^2)(80)= (80)(10m/s^2)(2.5sin30)
thus as 1000J KE = 1000J PE at top.
thus his calculation is correct if friction is neg. -
I guess the correct statement is:Originally posted by starmoonsun:A crate of mass 80kg sits on the floor. the crate must be brought to the top of a loading dock by sliding it up a ramp 2.5m long, inclined at 30 degrees. the worker, giving no thought to the force of friction, calculates that he can get the crate up the ramp by giving it an initial speed of 5m/s at the bottom and letting it go. unfortunately, friction is negligible, the crate slides up 1.6m on the ramp, stops, and slides back down.
using conservation of energy, show that the initial speed of 5.om/s as calculated by the worker is correct if friction is negligible
unfortunately, friction is NOT negligible, the crate slides up 1.6m on the ramp, stops, and slides back down.
If friction is negligible (usually the case for O levels), then we can use conservation of energy.
initial kinetic energy = final increase in potential energy
because the ramp is angled at 30 degrees and is 2.5 m long, the height increase is 2.5 sin 30 = 1.25m
1/2 m v^2 = m (1.25) (10)
v^2 = 25
Hence v = 5 m/s -
Hmm this is not secondary standard right?Originally posted by starmoonsun:A crate of mass 80kg sits on the floor. the crate must be brought to the top of a loading dock by sliding it up a ramp 2.5m long, inclined at 30 degrees. the worker, giving no thought to the force of friction, calculates that he can get the crate up the ramp by giving it an initial speed of 5m/s at the bottom and letting it go. unfortunately, friction is negligible, the crate slides up 1.6m on the ramp, stops, and slides back down.
using conservation of energy, show that the initial speed of 5.om/s as calculated by the worker is correct if friction is negligible -
O levelOriginally posted by jlzk:Hmm this is not secondary standard right? -
Oh no!!! O lvl...I am crying soon...cant believe it...how come sin is involve...oh god!
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Coz of that stupid 30 degrees thats why.Originally posted by jlzk:Oh no!!! O lvl...I am crying soon...cant believe it...how come sin is involve...oh god!
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Forgotten all of these.
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trigonometry to get the vertical height...Originally posted by jlzk:Oh no!!! O lvl...I am crying soon...cant believe it...how come sin is involve...oh god!
Reason being: Gravitational Potential Energy is a conservative force. Which means that no matter your path taken to reach that particular location, the final change in GPE still depends on the change in height, and not distance. -
=( so chim....waaa stress.!!!
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dun worry... just post your queries here in this forumOriginally posted by jlzk:=( so chim....waaa stress.!!!