An older model car accelerates from rest to speed v in 10 seconds. A newer, more
ID: 1572052 • Letter: A
Question
An older model car accelerates from rest to speed v in 10 seconds. A newer, more powerful sports car accelerates from rest to speed 2v in half the time (5 seconds). What is the ratio of the power of the newer car to that of the older car? 0.125 1.0 4.0 8.0 Discuss whether any work is being done by each of the following agents and, if so, whether the work is positive or negative. a chicken scratching on the ground a person studying physics a crane lifting a bucket of concrete the gravitational force on the bucket in the leg muscles of a person in the act of sitting down All of them do work. Positive work Is done in cases (i), (ii), and (iii) and negative work is done in cases (iv) and (v). No work is done in case (ii). Positive work is done in cases (i) and (iii) and negative work is done in cases (iv) and (v). No work is done in cases (i) and (ii). Positive work is done in case (iii) and negative work is done in cases (iv) and (v). No work is done in cases (i) and (ii). Positive work is done in cases (iii) and (v) and negative work is done in case (iv). A block of mass m is projected across a horizontal surface with an initial speed v. It slides until it stops due to the friction force between the block and the surface. The same block Is now projected across the horizontal surface with an initial speed v/2. When the block has come to rest, how does the distance from the projection point compare to that in the first case? It Is the same. It Is half as large. It Is one fourth as large. It Is none of these.Explanation / Answer
question23 : option C = 4.0 (power is equal to force into speed)
question 24:optionB
work is considered as positive ,if the direction of displacementof the body on which the force is acting is same as that of the direction of force
whereas negative when the displacement of the body on which the force is acting is in opposite to the direction of force.
question 25 :option c : ( one fourth of the first case)
change in kinetic energy = work done= Force x displacement
change in KE of the second case = 0.25 times that of the change in KE of the first case
hence displacement of the second case = 0.25 times that of the displacement achieved by the first case