NEET Laws of Motion MCQs & PYQs

When kinetic energy of the system is zero, speed of objects will be zero so momentum will always be zero.

Whereas momentum being a vector quantity may be zero when directions of velocities cancel each other. so speed and kinetic energy may of may not be zero when momentum is zero

This is due to inertia of motion. 

Given momentum of the object is P = a + bt²;

Force is defined as rate of change of momentum F= dP/dt= 2bt. so Force is proportional to t.

Force is defined as rate of change of momentum ie. F= dP/dt= change in momentum / time

Here Force = (mv-mu)/t= m(v-u)/t= 1 kg (0- 5)/ 5 = 1 N

Momentum of object is given as, P = 2cos tˆi + 2sin t ˆj , 

From Newtons Second law, F = dP/dt = -2 sin t î + 2 cos t ˆj.

Taking Dot product of P and F we get = -4 sint . cos t + 4 sint .cost =0 .

So, force and momentum are perpendicular to each other.

Maximum resultant force will act on the object when 6N and 8 N forces will be acting in same direction. F max= 14 N.

Maximum Acceleration= Maximum Force/ mass= 14 N/ 7 kg = 2m/s²

Due to inertia of direction person inside the bus has a tendency to move in a straight line. In case of sudden turn body ties to maintain its linear motion.

Impulse is change in momentum so, J = F.dt = 200 × 0.25 =50 N-s

According to Newtons second law of motion

F= v. dm/dt

so, acceleration = v. (dm/dt)/m

⇒ 20 m/s² = 1000 ×(dm/dt)/6000

⇒dm/dt = 120 kg/sec

Net Force acting on the block in upward direction is 4T which will balance weight of the object. So, 

⇒ 4T= 800 N 

⇒T = 200 N