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3 years ago

7

before dancing on a smooth wooden floor, ballet dancers sometimes sometimes put a sticky powered called rosin on their shoes sol

es. Why? what force are they taking advantage of?

1 answer:

Nookie1986 [14]3 years ago

3 0

Answer:

Hi

Explanation:

the dancers wish to increase their grip which takes advantage of the force of friction.

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A wave travels at 13 m/s and the crests are 6 meters apart. How many waves would you see pass you by per second? (round up to th

MrRa [10]

Answer:Number of waves =2.2

Explanation:

The frequency of A wave is defined as the number of waves moving a fixed point per second which is given as

f= $\frac{N}{t}$

F= Frequency

N= number of waves

t= time

We first find the frequency

Given velocity of the wave, v = 13m/s

and wavelength, λ as 6meters(distance between two consecutive crest)

, we fiind the frequency using

v= f λ

frequency = v / λ

= (13m/s ) / 6

=2.16s-1

f = $\frac{N}{t}$

2.16s₋¹= $\frac{N}{1s}$

Therefore N, Number of waves = 2.16 waves rounded up to 2.2 waves

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3 years ago

A cylindrical rod 21.5 cm long with a mass of 1.20 kg and a radius of 1.50 cm has a ball of diameter of 6.90 cm and a mass of 2.

Sergeeva-Olga [200]

Answer

given,

length of rod = 21.5 cm = 0.215 m

mass of rod (m) = 1.2 Kg

radius, r = 1.50

mass of ball, M = 2 Kg

radius of ball, r = 6.90/2 = 3.45 cm = 0.0345 m

considering the rod is thin

$I = \dfrac{1}{3}M_{rod}L^2 + [\dfrac{2}{5}M_{ball}R^2+M_{ball}(R+L)^2]$

$I = \dfrac{1}{3}\times 1.2 \times 0.215^2 + [\dfrac{2}{5}\times 2 \times 0.0345^2+2\times (0.0345 +0.215)^2]$

I = 0.144 kg.m²

rotational kinetic energy of the rod is equal to

$KE = M_{rod}g\dfrac{L}{2} + M_{ball}g(L+R)^2$

$KE = 1.2 \times 9.8 \times \dfrac{0.215}{2} + 2\times 9.8\times (0.215+0.0345)^2$

KE = 6.15 J

b) using conservation of energy

$K_f + U_f = K_i + U_i + \Delta E$

$\dfrac{1}{2}I\omega^2+ 0=0 + 6.15+0$

$\dfrac{1}{2}\times 0.144 \times \omega^2= 6.15$

ω = 9.25 rad/s

c) linear speed of the ball

v = r ω

v = (L+R )ω

v = (0.215+0.0345) x 9.25

v =2.31 m/s

d) using equation of motion

v² = u² + 2 g h

v² = 0 + 2 x 9.8 x 0.248

v = √4.86

v =2.20 m/s

speed attained by the swing is more than free fall

% greater = $\dfrac{2.31-2.20}{2.20}\times 100$

= 5 %

speed of swing is 5 % more than free fall

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