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3 years ago

What is the change in the internal energy of a system that does 400 joules of work and absorbs 700 joules of heat?

1 answer:

3 0

When a system uses up 400 J (or does 400 J of work), this means the internal energy decreases by 400 J. When it absorbs 700 J of heat, it means 700 J is added to total internal energy present.

Thus, we have a total change of -400 + 700 = 300 J in the internal energy of the system.

Answer: 300 J

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A 3kg chunk of putty moving at a speed of 5 m/a collides with, and sticks to, a 5kg. bowling ball that is initially at REST. The

astraxan [27]

You'd have an easier time using the equation if you understood where the equation comes from.

The law here ... the major principle to remember, the key, the fundamental truth, the big cookie ... is the fact that momentum is conserved. The total momentum after they join up is the same as the total momentum before they meet.

Momentum of an object is (mass) times (speed).

Now, list all the things you know, before and after the putty meets the ball:

Before: There are two objects.
Mass of putty = 3 kg
Speed of putty = 5m/s
Momentum of putty = 3 x 5 = 15 kg-m/s.

Mass of ball = 5 kg
Speed of ball = zero
Momentum of ball = 5 x 0 = zero

Total momentum of both things = 15 kg-m/s

After: There is only one object, because they stuck together.
Mass of (putty+ball) = (3+5) = 8 kg
Speed of (putty+ball) = we don't know; that's what we have to find

Momentum of (putty+ball) = 8 x (speed)

===================================

We know that the momentum after is equal to the momentum before.

8 x (speed) = 15 kg-m/s

Divide each side by 8 :

Speed = 15 / 8 = 1.875 m/s  after they stick together.

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4 years ago

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3 years ago

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4 years ago

A 20 gram bullet, traveling horizontally with a velocity of magnitude 350 m/s, is fired into a wooden block with a mass of 0.75,

sertanlavr [38]

Answer:

The kinetic energy is 10.65 joules.

Explanation:

This case can be considered as a collision if we neglect the frictional forces the ball experiences traveling through the wooden block because are lower than the impact forces, then we can use conservation of linear momentum to model this situation considering the system block-bullet.

Linear momentum states total initial momentum (pi) is equal to the final momentum (pf), this is:

$p_f=p_i$

Total momentum is the sum of individual momentums, in our case the momentum of the ball (pb) plus the momentum of the wooden block (pw), then:

$p_{bf}+p_{wf}=p_{bi}+p_{wi}$

Linear momentum of an object is defined as mass times velocity, then:

$m_bv_{bf}+m_wv_{wf}=m_bv_{bi}+m_wv_{wi}$

With vb the velocities of the bullet, mb the mass of the bullet, vw the velocities of the wooden block and mw the mass of the wooden block. Note that the wooden block is initially at rest, that means the initial velocity of the wooden block is zero, then:

$m_bv_{bf}+m_wv_{wf}=m_bv_{bi}$

Solving the equation for the final velocity of the block:

$v_{wf}=\frac{m_bv_{bi} - m_bv_{bf}}{m_w}=\frac{m_b(v_{bi} - v_{bf})}{m_w}$

$v_{wf}=\frac{0.02(350- 150)}{0.75} =5.33 \frac{m}{s}$

(Important: i. The sign of the velocities is important, so we chose positive direction as the direction the bullet moves initially, positive velocities means they are in this same direction.

ii. I assume 0.75 kg for the mass of the wooden block because you didn't provide its unities)

Now with the velocity of the bullet after the collision we can find the kinetic energy using the equation for kinetic energy:

$K=\frac{m_wv_{wf}^2}{2}=\frac{(0.75)(5.33)^2}{2}$

$K=10.65 J$

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3 years ago

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