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wolverine [178]
3 years ago
6

1. Astronomical observatories have been available since ancient times, and many cultures set aside special sites for astronomica

l observations. The thing modern observatories have that was missing from these older observatories until about 1610 was: a. a dark site, where lights did not get in the way b. graduate students or other assistants for sharing the astronomer’s work c. a method of keeping good records d. a way of measuring from what general direction in the sky a beam of light was coming e. telescopes
Physics
1 answer:
nydimaria [60]3 years ago
4 0

Answer:

e telescopes

Explanation:

may i be marked brainliest?

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3 years ago
A box is placed on a 30o frictionless incline. What is the acceleration of the box as it slides down the incline
balandron [24]

Answer:

<em>2.78m/s²</em>

Explanation:

Complete question:

<em>A box is placed on a 30° frictionless incline. What is the acceleration of the box as it slides down the incline when the co-efficient of friction is 0.25?</em>

According to Newton's second law of motion:

\sum F_x = ma_x\\F_m - F_f = ma_x\\mgsin\theta - \mu mg cos\theta = ma_x\\gsin\theta - \mu g cos\theta = a_x\\

Where:

\mu is the coefficient of friction

g is the acceleration due to gravity

Fm is the moving force acting on the body

Ff is the frictional force

m is the mass of the box

a is the acceleration'

Given

\theta = 30^0\\\mu = 0.25\\g = 9.8m/s^2

Required

acceleration of the box

Substitute the given parameters into the resulting expression above:

Recall that:

gsin\theta - \mu g cos\theta = a_x\\

9.8sin30 - 0.25(9.8)cos30 = ax

9.8(0.5) - 0.25(9.8)(0.866) = ax

4.9 - 2.1217 = ax

ax = 2.78m/s²

<em>Hence the acceleration of the box as it slides down the incline is 2.78m/s²</em>

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A bicycle rider travels 50.0 km in 2.5 hours. What is his average speed?
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