A body is thrown vertically upwards. Which one of the following graphs correctly represent the velocity vs time?
A.
Velocity at any time t is given by
v = u + at
v = v0 + (–g)t
v = v0 – gt
Straight line negative slope.
A point p moves in counter -clockwise direction on a circular path as shown in the figure. The movement of P is such that it sweeps out the length s = t3 + 5, where s is metre and t is in second. The radius of the path is 20 m. The acceleration of P when t =2 s is nearly
13 ms-2
12 ms-2
7.2 ms-2
7.2 ms-2
D.
7.2 ms-2
Given that, s =t3 +5
therefore speed v, = ds/st = 3t2
and rate of change of speed, at = dv/dt = 6t
∴ Tangential acceleration at t =2s
at = 6 x 2 = 12 ms-1
and at t = 2s, v = 3 (2)2 = 12 ms-1
∴ Centripetal acceleration, ac = v2/R = 144/20 ms-2
∴ Net acceleration = 
A time-dependent force F = 6t acts on a particle of mass 1 kg. If the particle starts from rest, the work done by the force during the first 1 sec. will be
9J
18 J
4.5 J
4.5 J
C.
4.5 J
F = 6t = ma
⇒ a = 6t
A body of mass m = 10–2 kg is moving in a medium and experiences a frictional force F = –kv2. Its initial speed is v0 = 10 ms–1. If, after 10 s, its energy is 1/8 mv02,the value of k will be
10-4 kg m-1
10–1 kg m–1 s–1
10-3 kg m-1
10-3 kg m-1
A.
10-4 kg m-1
Switch
and an acceleration of It speed 
after 10 s
