Answer TRUE OR FALSE 17) Kinetic energy is proportional to speed. 18) The work r

Question

Answer TRUE OR FALSE

17) Kinetic energy is proportional to speed.   

18) The work required to stretch a spring changes linearly with the amount of stretch.

19) If a force is directed perpendicular to the displacement, no work is done by that force.

20) A force can be exerted on an object and yet do no work.

21) Work is a vector quantity.

22) In an inelastic collision, the initial kinetic energy is less than the final kinetic energy.

23) The impulse delivered to an object is equal to the change in the object's velocity.

24) In a one-dimensional elastic collision of two identical masses, the masses always exchange velocities.

25) In any elastic head-on collision, the relative speed of the two objects after the collision has the same magnitude (but opposite direction) as before the collision, no matter what the masses are.

Explanation / Answer

17) Kinetic energy is proportional to speed?

Ke = 1/2 x Mass xVelocity2

KE=1/2mv2

. Speed and velocity are not the same. Velocity is a vector (and thus, so is Ke) since velocity has a direction associated with it. Speed is not a vector quantity, but is only the magnitude of the velocity.

The equation for kinectic energy is based on Velocity, and not on Speed,

so the answer isFALSE

18) The work required to stretch a spring changes linearly with the amount of stretch? true or false

Work = Force x Distance (1)
and
Spring Force = Spring Constant x Distance Streched (2)

So, substituting (2) into (1)

Work = (Spring Constant xDistance) xDistance

Work = Spring Constant x(Distance2)

So work increase as a function of the distance squared, not linearly,

so the answer is FALSE

19)The work done by a force can be positive or negative. If the component of the force in the direction of the displacement is positive, the work is positive, and if the component of the force in the direction of the displacement is negative, the work is negative. If the force is perpendicular to the displacement then it does no work.

so answer is true

21) Work is a scalar,.

The SI unit of work Nm = Joule (J)

W = F·d is the work done by a constant force.

W is the scalar product or "dot product" of the force and the displacement vectors. The scalar product of two vectors A and B is a scalar quantity (a number with units) equal to the product of the magnitudes of the two vectors and the cosine of the smallest angle between them.

A·B = ABcos.

So answer is FALSE

20)A force acting on an object does no work if IT IS PERPENDICULAR TO THE DIRECTION OF THE OBJECT'S MOTION.

If it's at an angle, it does work W = Fd cos

So answer is true

22)in an inelastic collision the final kinetic energy is always less than initial kinetic energy

So answer is false

23) The impulse delivered to an object is not equal to the change in the object's velocity

So answer is false

24) In a one-dimensional elastic collision of two identical masses, then the masses always exchange velocities.

In other words, if the masses are equal, the two objects simply exchange velocities in an elastic collision.

C. m1 = m2, v2 = 0:

So the answer is true

25) In any elastic head-on collision, the relative speed of the two objects after the collision has the same magnitude (but opposite direction) as before the collision, no matter what the masses are.

So the answeris false

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