Ask question

Ask question

All categories

3 years ago

10

John runs for 10 mins at a uniform speed 9kn/h. At what speed should he run for the next 20mins so that theaverage speed comes t

o 12km/h.

1 answer:

kolbaska11 [484]3 years ago

4 0

Answer:

13.5 km/h

Explanation:

John runs for 10 min at 9 km/h, then 20 min at v. He will have run a total of 30 min at 12 km/h.

Therefore:

(30 min) (12 km/h) = (10 min) (9 km/h) + (20 min) v

v = 13.5 km/h

You might be interested in

In the Bohr model of the hydrogen atom, an electron moves in a circular path around a proton. The speed of the electron is appro

Alexxx [7]

Explanation:

It is given that,

Radius of the circular orbit, $r=0.53\times 10^{-10}\ m$

Speed of the electron, $v=2.2\times 10^6\ m/s$

Mass of the electron, $m=9.1\times 10^{-31}\ kg$

(a) The force acting on the electron is centripetal force. Its formula is given by :

$F=\dfrac{mv^2}{r}$

$F=\dfrac{9.1\times 10^{-31}\times (2.2\times 10^6)^2}{0.53\times 10^{-10}}$

$F=8.31\times 10^{-8}\ N$

(b) The centripetal acceleration of the electron is given by :

$a=\dfrac{v^2}{r}$

$a=\dfrac{(2.2\times 10^6)^2}{0.53\times 10^{-10}}$

$a=9.13\times 10^{22}\ m/s^2$

Hence, this is the required solution.

5 0

3 years ago

What is happening inside muscles when they become sore?

Verizon [17]

Answer:

When muscles are required to work harder than they're used to or in a different way, it's believed to cause microscopic damage to the muscle fibres, resulting in muscle soreness or stiffness. DOMS is often mistakenly believed to be caused by a build up of lactic acid, but lactic acid isn't involved in this process.

Explanation:

4 0

3 years ago

Explain how a projectile might be modified to decrease the air resistance impacting its trajectory.

Vitek1552 [10]

Answer:

Explanation:

Explain how a projectile might be modified to decrease the air resistance impacting its trajectory.

5 0

3 years ago

Condensation happens when moist air ____. A. gains heat by radiation and warms B. warms adiabatically as it sinks to a lower ele

alina1380 [7]

Answer:

C. cools adiabatically as it sinks to a lower elevation

Explanation:

Condensation is the phenomenon where there is a change of the state of matter from gas phase to liquid phase. Vaporization is the reverse of condensation. If a process occurs without the transfer of heat and mass of a thermodynamic system with its surroundings then it is known as an adiabatic process.

Moist air consists of water in gaseous state, so when it is cooled without any exchange of mass or heat there is change of phase.

5 0

3 years ago

In a ballistic pendulum experiment, projectile 1 results in a maximum height h of the pendulum equal to 2.6 cm. A second project

Trava [24]

Answer:

Second projectile is 1.4 times faster than first projectile.

Explanation:

By linear momentum conservation

Pi = Pf

m x U + M x 0 = (m + M) x V

$U= \dfrac{(m + M)\times V}{m}$

Now Since this projectile + pendulum system rises to height 'h', So using energy conservation:

KEi + PEi = KEf + PEf

PEi = 0, at reference point

KEf = 0, Speed of system zero at height 'h'

$KEi = \dfrac{(m + M)\times V^2}{2}$

PEf = (m + M) g h

So,

$\dfrac{(m + M)\times V^2}{2} + 0 = 0+ (m + M) g h$

$V =\sqrt {2gh}$

So from above value of V

Initial velocity of projectile =U

$U=\dfrac{(M+m)\sqrt{2gh}}{m}$

Now Since mass of projectile and pendulum are constant, So Initial velocity of projectile is proportional to the square root of height swung by pendulum.

Which means

$\dfrac{U_2}{U_1}=\sqrt{\dfrac{h_2}{h_1}}$

$U_2=\sqrt{\dfrac{h_2}{h_1}}\times U_1$

$U_2=\sqrt{\dfrac{5.2}{2.6}}\times U_1$

U₂ = 1.41 U₁

Therefore we can say that ,Second projectile is 1.4 times faster than first projectile.

4 0

3 years ago