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pav-90 [236]
3 years ago
12

A 7.80 g bullet moving at 530 m/s penetrates a tree trunk to a depth of 5.40 cm. (a) Use work and energy considerations to find

the average frictional force that stops the bullet. (b) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.
Physics
1 answer:
True [87]3 years ago
8 0

Answer:

a) F=20287.22N

b) t=2*10^-4s

Explanation:

E=1/2*m*v^2=0.5*7.8*10^-3kg*(530m/s)^2=1095.51J

The frictional force's work must be equal than the energy to stop the bullet.

So: W=F*d=F*0.054m=1095.51J, F=20287.22N

Considering the frictional force is constant, the bullet moves with constant aceleration.

a=F/m=20287.22N/7.8*10-2kg=2.6*10^6m/s^2

then d(t)=Vt-1/2*a*t^2,

5.4*10^-2m=530m/s*t-1.3*10^6m/s^2*t^2

I will calculate the time using the cuadratic formula:

\frac{-b+-\sqrt{b^{2}-4ac } }{2a}

with a=1.3*10^6, b=-530, c=5.4*10^-2

t=2*10^-4s

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Answer:

a) 0 metres

b) From time 0 s to 10 s , the car was accelerated. Its velocity accelerated from 0m/s to 20 m/s

c) 20 m/s

Explanation:

a) <em>Formula of displacement= velocity x time</em>

time=40 s

velocity =0 m/s

∴ displacement= 0 x 40 = 0 m

Magnitude of displacement is 0 m

b) The increase in velocity shows that there has been acceleration.

c) The average velocity of the car is =\frac{0+40}{2\\}   {initial velocity + final velocity}

                                                            =\frac{40}{2}

                                                             =20

Therefore, the magnitude of the average velocity  of the car is 20 m/s

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Answer:

Acceleration of the meteorite, a=-38409.09\ m/s^2

Explanation:

It is given that,

A Meteorite after striking struck a car, v = 0

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a=\dfrac{v^2-u^2}{2s}

a=\dfrac{-(130)^2}{2\times 0.22}

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So, the deceleration of the Meteorite is -38409.09\ m/s^2. Hence, this is the required solution.

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