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3 years ago

How far can a girl run in 15 min. if she runs at an avg speed of 16 km/hr? (Hint: Remember to convert minutes to hours.)

Physics

1 answer:

Dmitriy789 [7]3 years ago

4 0

Answer:

Explanation:

We know the equation,

Speed = distance / time

But here it's mentioned the average speed, so the equation can be rewritten as,

Average speed = total distance/time taken

And we get,

Total distance = average speed × time taken

So we get by substituting,

Total distance = 16km/h × (15min/60)

= 4 km

Mind that I have converted time to hours by dividing by 60.

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Questions 15 out of 20

Olin [163]

Answer:

Explanation:

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4 years ago

If 1.8 amp flows through a 40 ohm resistor, the voltage across the resistor is :

GenaCL600 [577]

Answer:

72 volts.

Explanation:

To solve this, we have to use the Ohm's law.

The ohm's law tells us that the voltage drop of a resistor is directly proportional to the current applied to the conductor.

$V=I*R$

in this case the current is 1.8 amps and the resistor is 40 ohm

$V=1.8*40$

$V=72 volts$ .

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4 years ago

Two people stand facing each other at roller skating rink then push off each other

9966 [12]

a) 0 kg m/s

b) 0 kg m/s

c) +3 m/s

d) 60 N

Explanation:

The momentum of an object is a vector quantity given by:

$p=mv$

where

m is the mass of the object

v is the velocity of the object

In this problem, we have a system of two people, so the total momentum will be the sum of the individual momenta of the two people:

$p=p_1 + p_2$

Which can be rewritten as

$p=m_1 u_1 + m_2 u_2$

where $m_1,m_2$ are the masses of the two people and $u_1,u_2$ their initial velocities.

However, the two people are initially at rest, so

$u_1 = 0\\u_2 = 0$

Therefore the total momentum is

$p=0+0=0$

The principle of conservation of momentum states that when there are no external forces acting on a system, the total momentum of the system is conserved, so we can write:

$p_i = p_f$

where

$p_i$ is the total momentum of the system before

$p_f$ is the total momentum of the system after

In this problem,

$p_i = 0$

As we calculated in part a: this is because the total momentum of the two people before they push off each other is zero.

Therefore, according to the law of conservation of momentum,

$p_f = p_i = 0$

So the total momentum is zero also after they push off each other.

The total momentum of the girl and the boy after they push off each other can be written as:

$p_f = m_1 v_1 + m_2 v_2$ (1)

where:

$m_1 = 30 kg$ is the mass of the girl

$v_1 = -5 m/s$ is her velocity (she moves backward, so the negative sign)

$m_2 = 50 kg$ is the mass of the boy

$v_2$ is the velocity of the boy

As calculated in part b), we also know that the total momentum of the girl and the boy is

$p_f = 0$ (2)

By combining eq(1) and eq(2) we get

$0=m_1 v_1 + m_2 v_2$

And solving for v2 we find the velocity of the boy:

$v_2=-\frac{m_1 v_1}{m_2}=-\frac{(30)(-5)}{50}=+3 m/s$

and the positive sign means he is moving forward.

We can solve this part by applying the impulse theorem, which states that the change in momentum of an object is equal to the product between the force applied on it and the duration of the collision:

$\Delta p = F\Delta t$