1 Answers
491.)no the speed of a particle can never be negative......this is because speed of a particle is the magnitude of its velocity and thus can never be negative..............also speed is a scalar quantity and can never be negative.......
2.)no......this cant be......when a particle has constant velocity,it means that it covers proportionate distances in a time interval however big or small....thus its instantaneous velocity and average velocity can never be negative...
3.)a)yes a body can have zero velocity and yet it can have acceleration.....for example when a body is thrown vertically up at highest point,its velocity is zero but it has downward acceleration equal to acceleration due to gravity
3.)b)no a body cannot have constant velocity and varying speed...it is because at constant velocity both the magnitude and direction of a body remains constant and so speed which is the magnitude of velocity is thus kept constant.......
4.) for the first stone,
u=0,a=g=10m/s2,s=h m,t=t s
thus, h=1/2(10)t2.................(i)
for the second stone,
u=14m/s, a=g=10m/s2, s=h m, t=(t-1)s
thus, h=14(t-1)+1/2(10)(t-1)2.................(ii)
equating (i) & (ii),
1/2(10)t2=14(t-1)+1/2(10)(t-1)2
or, 14t-14+5(1-2t)=0
or, t=9/4---------(iii)
thus,h=1/2(10)(9/4)2,
or, h=25.3125m(ans)
5.)as projectile is thrown vertically upwards,
(0)2=u2-2gh
or, h=u2/2g
or,u2/2g=200..............(i)
when thrown obliquely,maximum range attained at θ=45°.
so, R=u2sin2θ/g
=(u2/g)sin(2X45°)
=2u2/2g
=2X200 m=400m
so, answer is (b.)
subhomoy bakshi
hem sheela model school
durgapur