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Aleksandr [31]
2 years ago
13

Use the work-energy theorem to determine the force required to stop a 1000 kg car moving at a speed of 20.0 m/s if there is a di

stance of 45.0 m in which to stop it.
Physics
1 answer:
Vlad1618 [11]2 years ago
6 0

Answer:

4.44 kN in the opposite direction of acceleration.

Explanation:

Given that, the initial speed of the car is, u=20m/s

And the mass of the car is, m=1000 kg

The total distance covered by the car before stop, s=45m

And the final speed of the car is, u=0m/s

Now initial kinetic energy is,

KE_{i}=\frac{1}{2}mu^{2}

Substitute the value of u and m in the above equation, we get

KE_{i}=\frac{1}{2}(1000kg)\times (20)^{2}\\KE_{i}=20000J

Now final kinetic energy is,

KE_{f}=\frac{1}{2}mv^{2}

Substitute the value of v and m in the above equation, we get

KE_{f}=\frac{1}{2}(1000kg)\times (0)^{2}\\KE_{i}=0J

Now applying work energy theorem.

Work done= change in kinetic energy

Therefore,

F.S=KE_{f}-KE_{i}\\F\times 45=(0-200000)J\\F=\frac{-200000J}{45}\\ F=-4444.44N\\F=-4.44kN

Here, the force is negative because the force and acceleration in the opposite direction.

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3 years ago
A wire 3.22 m long and 7.32 mm in diameter has a resistance of 11.9 mΩ. A potential difference of 33.7 V is applied between the
Scorpion4ik [409]

Answer:

(a) Current is 2831.93 A

(b) 8.40A/m^2

(c) \rho =15.52\times 10^{-9}ohm-m

Explanation:

Length of wire l = 3.22 m

Diameter of wire d = 7.32 mm = 0.00732 m

Cross sectional area of wire

A=\pi r^2=3.14\times 0.00366^2=4.20\times 10^{-5}m^2

Resistance R=11.9mohm=11.9\times 10^{-3}ohm

Potential difference V = 33.7 volt

(A) current is equal to

i=\frac{V}{R}=\frac{33.7}{11.9\times 10^{-3}}=2831.93A

(B) Current density is equal to

J=\frac{i}{A}

J=\frac{2831.93}{4.20\times 10^{-5}}=8.40A/m^2

(c) Resistance is equal to

R=\frac{\rho l}{A}

11.9\times 10^{-3}=\frac{\rho \times 3.22}{4.20\times 10^{-5}}

\rho =15.52\times 10^{-9}ohm-m

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If a boat and its riders have a mass of 900 kg and the boat drifts in at 1.4 m/s how much work does sam do to stop it?
Rama09 [41]
The initial kinetic energy of the boat and its rider is
K_i =  \frac{1}{2} mv_i^2 =  \frac{1}{2}(900 kg)(1.4 m/s)^2=882 J

After Sam stops it, the final kinetic energy of the boat+rider is
K_f = 0 J
because its final velocity is zero.

For the law of conservation of energy, the work done by Sam is the variation of kinetic energy of the system:
W=K_f-K_i =0-882 J=-882 J
where the negative sign is due to the fact that the force Sam is applying goes against the direction of motion of the boat.
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3 years ago
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