Pls someone answer it's an exam I have only 15 mins it's in physics

A 4 kg object moving to the left collides with and sticks to a 3 kg object moving to the right. Which of the following is true o

madam [21]

Answer:

D. The motion cannot be determined without knowing the speeds of the objects before the collision.

Explanation:

This question is tricky! We know the object moving to the left has a greater mass than the one moving to the right. We'd assume they would move to the left because the leftwards object has a greater mass, right?

Not. So. Fast.

We can solve for the objects' final velocity using the formula for momentum, m₁v₁ + m₂v₂ = (m₁ + m₂)v .

Now here's where the trap is sprung: we don't think about the equation. This shows that the final velocity of the objects and the direction depends on both the mass of the objects and their initial velocity.

Basically, what if the 3 kg object is moving at 1 m/s and the 4 kg object is moving at –0.5 m/s? The objects would move to the right after the collision!

Do we know the velocity of these objects? No, right?

That means we can't determine the direction of their motion unless we know their initial, pre-collision velocity. This question is tricky because we look at the 4 kg vs. 3 kg and automatically assume the 4 kg object would dictate the direction of motion. That's not true. It depends on velocity as well.

I hope this helps you! Have a great day!

4 0

3 years ago

A pendulum is observed to complete 23 full cycles in 58 seconds. Use the definition of frequency to find the frequency.

Alex17521 [72]

Answer: f = 0.397 Hz

Explanation:

f = cycles per second

f = 23 / 58 = 0.39655...

4 0

3 years ago

Consider a ball of mass m attached to a spring of stiffness k, oscillating with amplitude A on a frictionless horizontal surface

-Dominant- [34]

Answer:

Explanation:

Given

mass of ball is m

Spring constant is k

If a ball is undergoing a SHM motion then the total energy associated with it is

Total Energy $T=\frac{1}{2}kA^2$

where A=maximum Amplitude

Elastic Potential Energy of the system at any moment is given by

$U=\frac{1}{2}kx^2$

where x=compression in the spring

moment at which kinetic(K) and potential energy(U) are equal

i.e. $K=U$

Total energy $=K+U$

$\frac{1}{2}kA^2=2U$

$\frac{1}{2}kA^2=\frac{1}{2}kx^2$

$A^2=2x^2$

$x=\frac{A}{\sqrt{2}}$

i.e. at x=0.707 A kinetic energy and potential energy are equal

5 0

3 years ago

A spring hangs from the ceiling with an unstretched length of x 0 = 0.69 m x0=0.69 m . A m 1 = 7.5 kg m1=7.5 kg block is hung fr

sergejj [24]

Answer:

x2=0.732m

Explanation:

We can calculate the spring constant using the equilibrium equation of the block m1. Since the spring is in equilibrium, we can say that the acceleration of the block is equal to zero. So, its equilibrium equation is:

$m_1g-k\Delta x_1=0\\\\\implies k=\frac{m_1g}{\Delta x_1}\\\\k=\frac{(7.5kg)(9.8m/s^{2})}{0.84m-0.69m}=490N/m$

Then using the equilibrium equation of the block m2, we have:

$m_2g-k\Delta x_2=0\\\\\\implies x_2=x_0+\frac{m_2g}{k} \\x_2=0.69m+\frac{(2.1kg)(9.8m/s^{2})}{490N/m}= 0.732m$

In words, the lenght x2 of the spring when the m2 block is hung from it, is 0.732m.

6 0

3 years ago

A capacitor consists of a set of two parallel plates of area A separated by a distance d. This capacitor is connected to a batte

vovikov84 [41]

<h2>Answer:</h2>

(e) halved

<h2>Explanation:</h2>

The electrical enery (E) stored in a capacitor is related to its capacitance (C) and potential difference (V) as follows;

E = $\frac{1}{2}$ x C x $V^{2}$ ------------------------(i)

Also, the capacitance (C) of a capacitor consisting of parallel plates is related to the area (A) of the plates and distance (d) between the plates as follows;

C = A x ε₀ / d ------------------------(ii)

Where;

ε₀ is the permittivity of free space.

Substituting equation (ii) into equation (i) gives;

E = $\frac{1}{2}$ x A x ε₀ / d x $V^{2}$ --------------------(iii)

From equation(iii)

When the potential difference (V) is constant, then the electrical energy (E) stored is inversely proportional to the distance between the plates. i.e

E = k / d ----------------(iv)

Where;

k = proportionality constant = $\frac{1}{2}$ x A x ε₀ x $V^{2}$ (which is the product of all constants)

Therefore from equation (iv);

=> E₁ x d₁ = E₂ x d₂ ---------------------------(v)

Where;

E₁ and E₂ are the initial and final values of the electrical energy stored.

d₁ and d₂ are the initial and final values of the distance between the plates.

So, when the distance is doubled, i.e.

d₂ = 2 x d₁

Substitute the value of d₂ into equation (v) to give;

=> E₁ x d₁ = 2 x d₁ x E₂

Divide through by d₁ to give;

=> E₁ = 2 x E₂

Make E₂ subject of the formula

=> E₂ = $\frac{1}{2}$ x E₁

Therefore, the electrical energy stored in the capacitor will be halved.

6 0

4 years ago

Pls someone answer it's an exam I have only 15 mins it's in physics​

Pls someone answer it's an exam I have only 15 mins it's in physics