A 1000 kg car is brought to rest in 5 seconds from 20 m per second. The braking force needed is:
A1000 N
B2000 N
C8000 N
D4000 N
Answer & Solution
Correct answer: D. 4000 N
1. Compute change in momentum: Δp = m·(v − u) = 1000·(0 − 20) = −20000 kg m per second.
2. Apply impulse-momentum theorem: F·t = Δp.
3. F = Δp / t = (−20000) / 5.
4. F = −4000 N (the minus sign means the force opposes motion).
5. The required magnitude is 4000 N.
6. Options A and B underestimate; D doubles wrongly.
_Source: Selina Concise Physics ICSE Class 9, Ch 3 'Laws of Motion' (aplustopper.com extract)_
Related questions
A constant force of 6 N acts for 4 s on a 2 kg body initially at rest. The kinetic energy A stone of mass 0.5 kg is whirled in a horizontal circle of radius 1 m at constant angularA car of mass 1000 kg accelerates from rest to 20 m s⁻¹ in 5 s on a level road. The net hoA man weighing 50 kg jumps off a stationary boat of mass 250 kg into water with a horizontNewton's third law states that 'action and reaction are equal and opposite'. The most accuTwo identical billiard balls strike a smooth rigid wall with equal speeds u. Ball A strikeA force F acts on a particle making an angle θ with its instantaneous velocity. The componA cricketer draws his hands back while catching a fast ball. The physical reason is that: