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Please solve these problems(Kinematics)?
1) An elevator is descending with uniform acceleration.To measure the acceleration, a person in the elevator drops a coin at the moment the elevator starts.The coin is 6 ft. above the floor of the elevator at the time it is dropped.The person observes that the coin strikes the floor in 1 second.Calculate from this data the acceleration of the elevator.
2)A ball is thrown horizontlly from a point 100m above the ground with speed 20m/s.Find (a) the time it takes to reach the ground, (b) the horizontal distance it travels before reaching the ground, (c) the velocity(direaction and magnitude) with which it strikes the ground.
Show all the steps for Question no. 1.
3 Answers
- nealjkingLv 61 decade agoFavorite Answer
1) Elevator
The elevator drops with acceleration a, so its apparent gravity is going to be g' = g-a
Since s = g't^2/2
6 = g'/2
so g' = 2*6 = 12
Therefore 12 = g' = g - a
so
a = g - 12
= 32 - 12 = 20
Therefore a = 20 ft/s^2
b) Ball
a) 100 = gt^2/2,
so t = sqrt(2´*100/g) = sqrt(200/g) = sqrt(200/9.8) = 4.52 s
b) horizontal distance = 20*t = 20*4.52 = 90.35 m
c) v-x = 20 m/s as before
v-y = gt = sqrt(200g) = sqrt(200*9.8) = 44.3 m/s
v = sqrt((v-x)^2 + (v-y)^2) = sqrt(20^2 + 44.3^2)
= 48.58 m/s
The angle from the vertical is
Atan(v-x/v-y) = Atan(20/44.3) = Atan(0.45)
= 24.3 degrees from straight down vertical
- Anonymous1 decade ago
i dont know.
