Physics, 31.07.2019 10:00, yahyaomf

2. a 200-kg boulder has 39,200 joules of gravitational potential energy. what height is it at? 3. a 1-kg model airplane has 12.5 joules of kinetic energy and 98 joules of gravitational potential energy. what is its speed? what is its height?

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We have that the gravitational energy is given by: U=mgh where m is the mass of the object (in kg), g is the gravitational acceleration and h is the height of the object (in meters). Hence, h=U/(m*g) where g=9.8 m/s^2. Thus, h=20 m if we substitute.
Similarly, substituting in b, we have that the height of the model plane is 10 m. The kinetic energy is given by: K= $\frac{1}{2} *m*u^2$ where u is the speed of the object. Hence, solving for u we have u= $\sqrt{2K/m}$ . Substituting, we have that u=5m/s.

answered: kmontello5

As per the first question we have to calculate the height at which the boulder is present.

we have been given the mass of the boulder [m] as 200 kg.

The gravitational potential energy is given as 39,000 Joule.

The gravitational potential energy at a height ' h' from the surface earth is given as P.E= mass×height×acceleration due to gravity

The value of g=9.8 m/s^2

Hence height [h] $=\frac{P.E}{mg}$

= $\frac{39000}{200*9.8} metre$

=19.8979 metre

As per the second question we have to calculate the sped and height of the model airplane.

the mass of model airplane is 1 kg

The kinetic energy [K.E] of the airplane is 12.5 joule

we have K.E $=\frac{1}{2} mass*speed^2$

K.E $=\frac{1}{2}mv^2$

$v^2=\frac{2K.E }{m}$

$v^2=\frac{2*12.5}{1}$

$v=\sqrt{25}$

v=5 m/s

Again we have to calculate the height [h]

The potential energy is given as 98 Joule.

we know that P.E= mgh

tex]h=\frac{P.E}{mg}[/tex]

= $\frac{98}{1*9.8} metre$

=10 metre

answered: Guest

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6 $\frac{m}{s^{2} }$

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s

answered: Guest

Answer59.2kg; /

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2. a 200-kg boulder has 39,200 joules of gravitational potential energy. what height is it at? 3. a...