Question

I. Multiple Choice Questions (4pts*5) Write a short explanation to justify your answer. 1. You are pushing a wooden crate with a force F across the floor at constant speed. You decide to turn the crate on end, reducing by half the surface area in contact with the floor. In the new orientation, to push the same crate across the same floor with the same speed, the force that you apply must be about a) 4F b) 2F c) F d) 1/2F e) 1/4F 2. A hockey puck is acted on by one or more forces, as shown in the of acceleration? a) A figure. In which case, the puck would experience the largest magnitude 3 N 5 N 7 N 3 N b) B c) C d) D 3 N 3 N 3 N a) A ement produces the largest overall extension? b) B c) c d) D 400 400 400

write a short explanation

Answer 1

1 )

Option C is correct.

because the frictional force is depends only on normal force and friction coefficient

and does not depend on the area of the contact.

f_s $\leq$ $\mu$ _sN

and

f_s = $\mu$ _kN

2 )

the net force is in case " A " is , 7 - 5 = 2 N

in case B ( 3² + 3² )^1/2 = 4.242 N

in case C ,

C_x = ( 3 + 3 cos45 ) = 5.12 N

C_y = 3 sin45 = 2.12 N

C = ( 5.12² + 2.12² )^1/2

C = 5.54 N

so the order is C > B > D > A

or

A < D < B < C

3 )

here also 400 N weight is hanged only in case " A "

next extension is in case " B "

next extension is in case " C "

next extension is in case " D "

A > B > C > D

So Option " A " is correct.