a stone is thrown vertically downwards with a speed of 10 m/s from a bridge. acceleration under gravity (9.8 m/s squared). the stone strikes the water 1.8 s later. from what height above the water was the stone thrown? assume 2 significant digits.

Answer 1

To solve this problem, we can use the equation of motion for vertical motion:

s = ut + 1/2 * at^2

where:
s = height
u = initial velocity
a = acceleration
t = time

In this case, the stone is thrown downwards, so the initial velocity u is -10 m/s (negative sign indicates the downward direction), acceleration a is -9.8 m/s^2 (negative sign indicates acceleration due to gravity), and the time t is 1.8 s.

Substituting these values into the equation:

s = -10 * 1.8 + 1/2 * (-9.8) * (1.8)^2

s = -18 - 8.82

s ≈ -26.82

Since the height cannot be negative, we take the magnitude of s:

height = |-26.82| ≈ 26.82 meters.

Therefore, the stone was thrown from a height of approximately 26.82 meters above the water.

Answer 2

a 55kg person is skating on the Rideadu canal. she reaches a maximum speed and then glides to a stop in 100 m. the coefficient between her skates and the ice is 0.010. what is the work done by kinetic friction?

Answer 3

To calculate the work done by kinetic friction, we can use the formula:

Work = Force * Distance

The force of kinetic friction can be calculated using the equation:

Force of Kinetic Friction = coefficient of friction * Normal Force

The normal force is equal to the weight of the person, which can be calculated as:

Weight = mass * acceleration due to gravity

Given:
Mass (m) = 55 kg
Coefficient of friction (μ) = 0.010
Distance (d) = 100 m
Acceleration due to gravity (g) = 9.8 m/s^2

First, calculate the weight:

Weight = mass * acceleration due to gravity
Weight = 55 kg * 9.8 m/s^2
Weight = 539 N

Next, calculate the force of kinetic friction:

Force of Kinetic Friction = coefficient of friction * Normal Force
Force of Kinetic Friction = 0.010 * 539 N
Force of Kinetic Friction = 5.39 N

Finally, calculate the work done:

Work = Force * Distance
Work = 5.39 N * 100 m
Work = 539 J

Therefore, the work done by kinetic friction is 539 Joules.