302 - Mechanics part 1 Questions Answers
A BODY STARTS WITH INITIAL VELOCITY 30m/s & A RETARDATION OF 4m/s2 . FIND THE DISTANCE TRAVELLED BY THE BODY IN 8th SECOND.
ANS 1m
by v = u - at
0 = 30 - 4t implies t = 7.5
it means velocity will become 0 in 7.5 sec.
distance covered in 7.5 sec. = 30*7.5 - 1/2*4*(7.5)2 = 225 - 225/2 = 225/2
distance covered in 7 sec. = 30*7 - 1/2*4*(7)2= 210 - 98 = 112
so distance covered in first half of eighth sec. = 112.5 - 112 = 0.5 m
distance covered in last half of eighth sec. = 0*0.5 + 1/2*4(0.5)2= 0.5
so total distance covered in eighth sec. = 0.5 + 0.5 = 1 meter
IN THE PREVIOUS QUES ( THAT WAS FROM ROTATn TOPIC , SUBMITTED 5 DAYS AGO) , I AM STILL NOT GETTING THE SOLn SUBMITTED BY YOU.
if this is the question based on number of rotations then read it carefully
A TOY CAR TRAVELS FROM A TO B AT A CONST. SPEED OF 20 km/h & IMMEDIATELY RETURNS TO A AT A CONST. SPEED v. IF THE AVG. SPEED OF THE CAR IS 24 km/h . THEN v IS = ?
total distance = d+d = 2d km.
total time taken = d/20 + d/v hours
so avg. speed = 2d/[d/20 + d/v]
or 24 = 2/[1/20 + 1/v]
or 12 = 1/[1/20 + 1/v]
or 1/20 + 1/v = 1/12
or 1/v = 1/12 - 1/20
or 1/v = 2/60
or v = 30
a coin placed on a gramophone record rotating at 33rpm flies off d record , if it is placed at a dist. of more than 16cmfrom d axis of rotation . If d record is revolving at 66rpm , the coin will fly off if it is placed a distance not less than ?
ans=4cm
coin will fly off, if it will gain the required centrifugal
so apply mrω2 = mRW2
a 1 kg block is attached (& held at rest with outside support) to free end of vertically hanging spring of force const. 10Ncm-1. when block is released wat max. extensn does it cause when it comes to rest instantaneously?
apply mgx = 1/2 kx2
for max. extension.
a block of mass m is suspended by a light thread from an elevator . the elevator starts moving up with a uniform acc . the work done during first t sec by tensn in thread ?
although i know how to calculate this ques . i.e w.d =Fds =m(g+a)Xds where ds=ut+1/2(at2) because acc is const a/c to ques BUT I want to know for ds why acc is a ,why not (a+g)
tension in the thread depends on g an a both.
but displacement covered by elevator depends only on the acceleration of the elevator, it does not depend upon the acceleration g thats why we do not use g in that case for finding displacement.
remember that in the problem we have to calculate work done by tension in the thread
FROM REST A BODY ROTATE 120 rotation/min FOR 20 sec THEN IT ROTATE FOR 5sec WITH SAME ROTATION . FIND HOW MANY ROTATn IT WILL MAKE?
ω = ω0+ αt
so 4π = 0 + α20 so α = π/5
so total angular displacement = 1/2 π/5 202 = 40 π = 20 rotation
and with angular velocity 2 rotation/sec total rotations in 5 sec. = 10
so answer will be 20+10 = 30
A hunter aims his gun at a monkey sitting on a tree at the instant bullet leaves the gun the monkey drops down . WILL THE BULLET HIT THE MONKEY ?
yes because monkey and bullet both are falling with the same gravity
consider a small segment of chain at angle β from top, its length = Rdβ and mass = mRdβ/L
its potential energy = [mRdβ/L]gRcosβ now integrate it within the limits 0 to L/R
for getting the answer of the second part calculate potential energy twice once between the limits 0 to L/R and then between the limits θ to θ+(L/R)
then difference of potential energy = KE of the chain. solve it ?
for getting third part differentiate v obtained in the second part with respect to t, dθ/dt will be ω and it will be v/R
finally put θ and t = 0 for getting the answer.
what is the formula for hole mobility in a semiconductor. ( not dimensional formula ,that i will find myself)
hole mobility = velocity of hole/electric field applied