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3 years ago

If a force on an object is aimed in the direction of the object’s velocity, the force does: a. no work.

1 answer:

6 0

Answer: If a force on an object is aimed in the direction of the object’s velocity, the force does positive work (b).

Explanation:

Hi, the answer is oprion b. positive work.

If a force on an object is aimed in the direction of the object’s velocity, the force does positive work.

An object's kinetic energy will only change if the force acting on the object changes the object's speed. This will only happen if there is a component of the force in the direction that the object moves.

So, A force will do work only if the force has a component in the direction that the object moves.

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A 4.2-g bullet is fired at a speed of 370 m/s into a stationary lead block, which moves a distance of 1.2 m before coming to res

Natali5045456 [20]

Answer:

(a) F = 239.575 N (b) t = 0.00649s or 6.49 ms

Explanation:

(a) By law of energy conservation, the bullet kinetic energy will be transferred to work done on stopping it from moving.

Formula for Kinetic Energy $E_k = \frac{mv^2}{2}$ where m is bullet mass, v is the velocity

Formula for work $W = FS$ where F is the average force and S is the distance travelled.

$E_k = W$

$\frac{mv^2}{2} = FS$

$F = \frac{mv^2}{2S}$

Substitute m = 4.2 g = 0.0042 kg, v = 370 m/s and S = 1.2 (m)

$F = \frac{0.0042*370^2}{2*1.2} = 239.575 N$

(b) If the force is constant, since the mass is constant and F = ma according to Newton's 2nd law, the acceleration on bullet is also constant

$a = \frac{F}{m} = \frac{239.575}{0.0042} = 57041.67 (m/s^2)$

We also have $v(t) = v_0 + at$

At the time the bullet is coming to rest, $v(t) = 0, a = -57041.67 m/s^2$

Therefore, $0 = 370 - 57041.67t$

$t = \frac{370}{57041.67} = 0.00649 s = 6.49 ms$

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4 years ago

What does the statement "all motion is relative"<br> mean?

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The statement that motion is relative is an important concept in physics. The meaning behind this statement is that the motion of an object is relative to either the frame of reference of the observer, or to another distinct frame of reference.

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3 years ago