A grindstone is initially spinning with an angular speed of 8.0 rad/s. The angul

Question

A grindstone is initially spinning with an angular speed of 8.0 rad/s. The angular speed is then increased uniformly to 10 rad/s over the next 4.0 seconds. The number of revolution that the grindstone turns through during this time is closest to: (1 rev = 2 pi rad) (a) 0.64 (b) 3.8 (c) 4.0 (d) 5.7 (e) 36 A string is tied to a doorknob 0.79 m from the hinge as shown in the figure. At the instant shown, the force F applied to the string is 5.0 N. The torque on the door is closest to: (a) 3.3 N.m (b) 2.2 N.m (c) 1.1 N.m (d) 0.84 N.m (e) 0.40 N.m Two pillars support a 4.0-m long diving board of negligible mass. One pillar is at the left end and the other pillar is 1.0 m away. The force F_1 exerted by the left pillar when a 51-kg diver stands at 1.2 m from the right end is closest to: (a) 800 N (b) 600 N (c) 900 N (d) 700 N (e) 500 N

Explanation / Answer

(1) ans

initial angular speed w1=8 rad/s

finial angular speed w2=10 rad/s

time t=4 sec

this concept belongs to the circular motion

w2^2-w162=2*(angular acceleration) $

10^2-8^2=2*(10-8)/t*2*pi*n

100-64=n

n=36

the correct option is E

(2) ans

distance S=0.79 m

force F=5 N

angle =57°

the torque t=FS sin(57)=5*0.79*sin(57)=3.323 N.m

3 ans

total upwards force=total down wards force

F1=mg

F1 =mg

F1*=51*9.8=500 N

the correct option E

4 ans

height h=1.8 m

the speed V={2gh/1+B}^1/2

={2*9.8*1.8/1+2/5]^1/2

= 5 m/s

F1=500

n=

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.