Homework answers / question archive / Question 1 Given vectors A with rightwards harpoon with barb upwards on top equals 2 i with hat on top space plus 3 j with hat on top space and B with rightwards harpoon with barb upwards on top equals 6 i with hat on top space plus space 9 j with hat on top space, what is the magnitude of the vector C with rightwards arrow on top equals A with rightwards arrow on top space bold cross times space B with rightwards arrow on top ? (hint: sketch the vectors

Question 1 Given vectors A with rightwards harpoon with barb upwards on top equals 2 i with hat on top space plus 3 j with hat on top space and B with rightwards harpoon with barb upwards on top equals 6 i with hat on top space plus space 9 j with hat on top space, what is the magnitude of the vector C with rightwards arrow on top equals A with rightwards arrow on top space bold cross times space B with rightwards arrow on top ? (hint: sketch the vectors

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Question 1

Given vectors A with rightwards harpoon with barb upwards on top equals 2 i with hat on top space plus 3 j with hat on top space and B with rightwards harpoon with barb upwards on top equals 6 i with hat on top space plus space 9 j with hat on top space, what is the magnitude of the vector C with rightwards arrow on top equals A with rightwards arrow on top space bold cross times space B with rightwards arrow on top ? (hint: sketch the vectors. Recall i with hat on top means "in the +x direction, j with hat on top "in the +y direction")

75

39

Zero

15

 

Question 2

An object, initially at rest, has a constant net torque τ applied to it for 8.00 s, and as a result gains a final kinetic energyK1.  How long should that same torque be applied to that same object for the kinetic energy to double (i.e., K2 =2K1)?

5.66 s

32.00 s

64.00 s

16.00 s

11.31 s

Question 3

Two solid disks have equal moments of inertia.  If the first disk's radius (R1) is one third of the second disk's radius (R2) , then what can you say regarding the disks' masses M1 and M2?

M1 = M2 /3

M1 = M2 /9

M1 = M2

M1 = 9M2

M1 = 3M2

Question 4

A solid sphere (like a bowling ball) and a hollow sphere (like a ping-pong ball) freely roll back and forth (without slipping) in identical circular tracks as shown below. They both start from rest at the same initial height H relative to thE bottom of the track.

(sofice)j (hollow sphere)

What can you say about the time it takes them to get to the bottom and how fast they are at the bottom? Ignore air resistance.

0 The solid sphere reaches the bottom first and its speed at the bottom is larger than the hollow sphere's

O The solid sphere reaches the bottom last and its speed at the bottom is larger than the hollow sphere's

 O The solid sphere reaches the bottom first and its speed at the bottom is smaller than the hollow sphere's

O The solid sphere reaches the bottom last and its speed at the bottom is smaller than the hollow sphere's

O Both the solid and the hollow sphere's reach the bottom at the same time and with the same speed

 

Question 5

At a certain instant, a rectangular block of mass m slides on a horizontal surface with speed V and a round object of the same mass m rolls on the surface with the same speed V. What can you say about the mechanical energies K block and K round of the objects?

0 k block > K round

0 K block < K round

0 Need to know the round object's mass, radius, and exact shape to answer

0 Cannot answer if the exact shape of the round object is not known

0 K block= K round

 

Question 6

A disk rotates around in axis passing through it’s center in the direction shown by the curvy arrow in the figure. As the rotation gradually down, what are the direction (x, y or z) and the sign (Positive or negative) of the disk angular acceleration.

0 ? in the +x direction, or in the – y direction

0 ? and or both in the –z direction         

0 ? in the –x direction or in the +x direction

0 ? and or both in the +z direction

0 ? or in the +z direction, or in the –z direction

 

 

Question 7

Consider the object below: two solid disks of identical size and mass, glued to each other side-by-side. The disks can rotate about one of these three axes: A passing through the center of one of the disks, B passing through the point where the disks touch each other, and C near the edge of the second disk.

Which of the floowing is correct order of the moments of inertia IA, IB and IC relative to each axis?

IB<IA<IC

IA<IB<IC

 IC<IB<IA

 IC=1A=Ib