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3 years ago

Pls help guys this is my 7th time posting XD

Physics

2 answers:

borishaifa [10]3 years ago

5 0

Answer:

Explanation:

initial velocity u = 54 km/h = 15 m/s

final velocity v = 18 km/h = 5 m/s

distance s = 10 m

1. v^2 = u^2 + 2as

5^2 = 15^2 + 2a × 10

25 = 225 + 20a

25 - 225 = 20a

20 a = -200

a = -200/2

a = -100m/s^2

∴Deacceleration = -100m/s^2

2. v = u + at

5 = 15 -100t

5-15 = -100t

-10 = -100t

t = 100 / 10

∴t = 10 sec

Total distance covered by the car 10 m

zysi [14]3 years ago

5 0

To me, the hardest part of this whole thing is keeping the units straight. We're starting out with information given to us in kilometers, hours, and meters, and we have to come up with answers in m/s² , seconds, and meters.

When I worked this problem, I jumped right in without thinking, and I immediately got bogged down when I had to go off to the side and convert some units.

Now I know better. THIS time, before we get all tangled up trying to solve anything, let's get clever and change everything to m/s right now !

(54 km/hour) · (1,000m/km) · (1 hour/3600 sec) = 15 meters/second

(18 km/hour) · (1,000 m/km) · (1 hour/3600 sec) = 5 meters/second

NOW I'll betcha it's gonna be about 70% faster and easier !

i). Acceleration = (change in speed / time for the change)

We know the distance, but not the time. I know there's a formula for it, but I've learned so many formulas during my lifetime that I can't remember ALL of them. So I just memorize some of them, and I work things out from the formulas that I know. Here's how I do time:)

Average speed during the given slow-down = (1/2)·(15+5) = 10 m/s

Distance covered during the given slow-down = 10 m.

Time = (distance) / (average speed) = (10m) / (10 m/s) = 1 second

Acceleration = (change in speed) / (time for the change)

Acceleration = (5 m/s - 15 m/s) / (1 second)

Acceleration = (-10 m/s) / (1 second)

Acceleration = -10 m/s² (or 'Deceleration' = 10 m/s² )

_____________________________________________

For parts ii). and iii)., there's a big shift in the question.

It only gave you the slow-down from 54 to 18 km/hr for the purpose of calculating the deceleration. NOW, for the rest of the answers, it's talking about a complete stop ... 0 m/s .

____________________________________________

ii). Time required to stop = (initial speed) / (deceleration)

Time to stop from 54 km/hr = (15 m/s) / (10 m/s²)

Time to stop = 1.5 seconds

iii). Distance covered = (average speed) · (time to stop)

Distance covered = (7.5 m/s) · (1.5 sec)

Distance covered = 11.25 meters

OR ... use the official formula:

Distance = (1/2) · (acceleration) · (time² )

Distance = (1/2) · (10 m/s²) · (1.5 sec)²

Distance = 11.25 meters yay !

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a 300kg motorboat is turned off as it approaches a dock and coasts towards it at .5 m/s. Isaac, whose mass is 62 kg jumps off th

Zolol [24]

-- Before he jumps, the mass of (Isaac + boat) = (300 + 62) = 362 kg,
their speed toward the dock is 0.5 m/s, and their linear momentum is

Momentum = (mass) x (speed) = (362kg x 0.5m/s) = 181 kg-m/s

relative to the dock. So this is the frame in which we'll need to conserve
momentum after his dramatic leap.

After the jump:

-- Just as Isaac is coiling his muscles and psyching himself up for the jump,
he's still moving at 0.5 m/s toward the dock. A split second later, he has left
the boat, and is flying through the air at a speed of 3 m/s relative to the boat.
That's 3.5 m/s relative to the dock.

His momentum relative to the dock is (62 x 3.5) = 217 kg-m/s toward it.

But there was only 181 kg-m/s total momentum before the jump, and Isaac
took away 217 of it in the direction of the dock. The boat must now provide
(217 - 181) = 36 kg-m/s of momentum in the opposite direction, in order to
keep the total momentum constant.

Without Isaac, the boat's mass is 300 kg, so

(300 x speed) = 36 kg-m/s .

Divide each side by 300: speed = 36/300 = 0.12 m/s , away from the dock.
=======================================

Another way to do it . . . maybe easier . . . in the frame of the boat.

In the frame of the boat, before the jump, Isaac is not moving, so
nobody and nothing has any momentum. The total momentum of
the boat-centered frame is zero, which needs to be conserved.

Isaac jumps out at 3 m/s, giving himself (62 x 3) = 186 kg-m/s of
momentum in the direction toward the dock.

Since 186 kg-m/s in that direction suddenly appeared out of nowhere,
there must be 186 kg-m/s in the other direction too, in order to keep
the total momentum zero.

In the frame of measurements from the boat, the boat itself must start
moving in the direction opposite Isaac's jump, at just the right speed
so that its momentum in that direction is 186 kg-m/s.
The mass of the boat is 300 kg so
(300 x speed) = 186

Divide each side by 300: speed = 186/300 = 0.62 m/s away from the jump.

Is this the same answer as I got when I was in the frame of the dock ?
I'm glad you asked. It sure doesn't look like it.

The boat is moving 0.62 m/s away from the jump-off point, and away from
the dock.
To somebody standing on the dock, the whole boat, with its intrepid passenger
and its frame of reference, were initially moving toward the dock at 0.5 m/s.
Start moving backwards away from that at 0.62 m/s, and the person standing
on the dock sees you start to move away from him at 0.12 m/s, and that's the
same answer that I got earlier, in the frame of reference tied to the dock.

yay !

By the way ... thanks for the 6 points. The warm cloudy water
and crusty green bread are delicious.

4 0

3 years ago

A mountain-climber friend with a mass of 74 kg ponders the idea of attaching a helium-filled balloon to himself to effectively r

bazaltina [42]

Answer:

$V=16.65 m^3$

Explanation:

The volume of the balloon can be find compared the force in each cases so:

reduce 25% from 74kg

$R=\frac{25}{100}*74kg=18.5kg$

So the net force uproad on the balloon is

$F_b=18.5kg*g$

Now the density of the both gases air and helium are different however the volume is the same change offcorss the mass so:

$P_h=\frac{m}{V}=0.179 kg/m^3$

$P_A=1.29 kg/m^3$

$F_b=F_A-F_H$

$F_b=m_a*g-m_h*g$

$m=P/V$

$18.5kg*g=(1.29kg/m^3-0.179kg/m^3*)V*g$

$V=\frac{18.5kg}{(1.29-0.179)kg/m^3}$

$V=16.65 m^3$

4 0

3 years ago

Which has more thermal energy: lake or a cup of hot chocolate?

lawyer [7]

Though the hot cocoa would have a higher temperature, the lake would have more thermal energy because it has more molecules with a greater total internal energy.

4 0

3 years ago

The 5-kg block A has an initial speed of 5 m/s as it slides down the smooth ramp, after which it collides with the stationary bl

Akimi4 [234]

Answer:

The coupled velocity of both the blocks is 1.92 m/s.

Explanation:

Given that,

Mass of block A, $m_1=5\ kg$

Initial speed of block A, $u_1=5\ m/s$

Mass of block B, $m_2=8\ kg$

Initial speed of block B, $u_2=0$

It is mentioned that if the two blocks couple together after collision. We need to find the common velocity immediately after collision. We know that due to coupling, it becomes the case of inelastic collision. Using the conservation of linear momentum. Let V is the coupled velocity of both the blocks. So,

$m_1u_1+m_2u_2=(m_1+m_2)V\\\\V=\dfrac{m_1u_1+m_2u_2}{(m_1+m_2)}\\\\V=\dfrac{5\times 5+0}{(5+8)}\\\\V=1.92\ m/s$

So, the coupled velocity of both the blocks is 1.92 m/s. Hence, this is the required solution.

8 0

3 years ago

A 4.0 kg object will have a weight of approximately 14.8 N on Mars. What is the gravitational field strength on M

Pie

Answer:

Gravitational field strength =weight/mass

Explanation:

14.8N/4.0kg

3.7N/kg

3 0

2 years ago

Pls help guys this is my 7th time posting XD​

Pls help guys this is my 7th time posting XD