Thread: Mechanics help please?

1) The Sun sets, fully disappearing over the horizon as you lie on the beach, your eyes 20 cm above the sand. You immediately jump up, your eyes now 170 cm above the sand, and you can again see the top of the Sun. If you count the number of seconds (t) until the Sun fully disappears again, you can estimate the radius of the Earth. Use the known radius of the Earth to calculate the time t.

2) Two students are asked to find the height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.2s, and the other, 2.6s. What % difference does the 0.4s make for the estimates of the building's height?

3) A small source of light S is located at a distance L from a vertical wall. An opaque object with a height of h moves toward the wall with constant velocity v1 of magnitude v. At time t= 0, the object is located at the source S. Find an expression for vs, the magnitude of the velocity of the top of the object's shadow, at time t. Express the speed of the top of the object's shadow in terms of t, v, L, and h.

Any and all help is greatly appreciated! (:

Originally Posted by Agneisse

1) The Sun sets, fully disappearing over the horizon as you lie on the beach, your eyes 20 cm above the sand. You immediately jump up, your eyes now 170 cm above the sand, and you can again see the top of the Sun. If you count the number of seconds (t) until the Sun fully disappears again, you can estimate the radius of the Earth. Use the known radius of the Earth to calculate the time t.

2) Two students are asked to find the height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.2s, and the other, 2.6s. What % difference does the 0.4s make for the estimates of the building's height?

3) A small source of light S is located at a distance L from a vertical wall. An opaque object with a height of h moves toward the wall with constant velocity v1 of magnitude v. At time t= 0, the object is located at the source S. Find an expression for vs, the magnitude of the velocity of the top of the object's shadow, at time t. Express the speed of the top of the object's shadow in terms of t, v, L, and h.

Any and all help is greatly appreciated! (:

These are quite clearly either homwork or take-home test problems.

You are on your own.

Try whatever you can before you post your schoolwork problems. After you've tried to solve them on your own, why not try posting what you've done with you're problems. You may get better feedback that way.

Glad to read such a nice piece of information.
This is exciting news.
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