exam in 2 days, find height of mountain?

[Starlight]

hey guys can you help me out with this one?

Can you help with (e)

I've given the answers for a-d

Professor cuthbert walks down the street, swining his plumb bob and timing it with a sto watch. Length of plumb bob is 30cm. In greenwich acceleration due to gravity is 9.80m/s2. Find the plumb bob period, freq of oscillation

1.10s, 0.910 hz

Earths g at gorund level vares at 9.78m/s^2 t 9.83 m/s^2 at top of north pole. Find the period at the equator and north pole

1.1098 at the poles, at the equator 1.1005s

Cuthbert is kidnapped and flown to an area of coast at sea level. He measures his period as 1.098s.Find radius of earth

6.372 x 10^6

(e) His kidnappers take him to a mountain and he measures the period as 1.09915s. How high is the mountain?

[availn]

Dat stopwatch xD

Just find g, and use that to find the another radius, just as you did when Cuthbert was at sea level. The difference between the two radiuses is the height of your mountain.

[Starlight]

Dat stopwatch xD

Just find g, and use that to find the another radius, just as you did when Cuthbert was at sea level. The difference between the two radiuses is the height of your mountain.

Thanks didn't realise it was that simple!

Just wondering if you would happen to know how to do this one too?

"Oil explorers set off explosives to make loud sounds, and listen to the echos. Physicists think there is oil under 500m deep Lake terror. Explorers detect a weak echo 0.94s after exploding dynamite at the surface of the water. Assuming that this is a reflection from the oil deposit, how deep will they have to drill into the granite to reach it? (speed of sound in granite is 6000 m/s)

Answer says 792 m