Kinetic energy has this unit?

A lead ball is dropped 30 feet from a church tower. If the acceleration due to gravity is 9.8m s^-2, how long does it take the b

Alika [10]

final velocity of a falling object = 0

and acceleration of a falling object is negative

now using the expression ( Newton's 3rd equation of motion)

${v}^{2} = {u}^{2} - 2gs$

where the parameters have their usual meaning

making

${u}^{2} \: the \: subject$

thus

${u}^{2} = 2gs$

$u = \sqrt{2gs}$

from the question,

g= 9.8m/s^2

s = 30m

substitute them into the equation

$u = \sqrt{2(9.8 \times 30)}$

$u = \sqrt{588}$

u = 24.25m/s

but the question is demanding for time but not the initial velocity

so substitute them in the

Newton's first equation of motion

where

V = u - gt

but from the question,

v= 0 and the acceleration is negative because it's a free fall

substitute the values into the equation

0 = 24.24 -9.8t

making t the subject

9.8t = 22.24

dividing through by 9.8

9.8t/9.8 = 22.24/9.8

t = 2.3s . therefore, it would take 2.3s for the ball to hit the ground.

4 0

4 years ago

A wooden disk of mass m and radius r has a string of negligible mass is wrapped around it. If the disk is allowed to fall and th

Tju [1.3M]

Answer:

$a = \frac{2}{3}g$

$T = \frac{mg}{3}$

Explanation:

As the disc is unrolling from the thread then at any moment of the time

We have force equation as

$mg - T = ma$

also by torque equation we can say

$TR = I\alpha$

$TR = \frac{1}{2}mR^2(\frac{a}{R})$

$T = \frac{1}{2}ma$

Now we have

$mg - \frac{1}{2}ma = ma$

$mg = \frac{3}{2}ma$

$a = \frac{2}{3}g$

Also from above equation the tension force in the string is

$T = \frac{1}{2}ma$

$T = \frac{mg}{3}$

7 0

4 years ago

What are the set of equations called that can be used to quantify motion in the case of uniform acceleration?

KATRIN_1 [288]

The kinematic equations are used to quantify motion in the case of uniform acceleration.

The other name is : SUVAT equations, where the letters signify:
displacement (s),
initial velocity (u),
final velocity (v),
acceleration (a), and
time (t).

There are three equations are attached in the picture: