10> A car is moving with a uniform velocity of 30 m/s. it is stopped in 2 se by applying a force of 1500 N through its brakes. Calculate (a) the change in momentum of the car (b) the retardation prod in the car and (c) the mass of the car. 11> A boy pushes a wall with a force of 20 N towards North. What force is exerted by the wall on the boy? 12 A block of mass 1.5 kg is hanging from rigid support by a string. What is the force exerted by the () block on the string (i) string on the block (g = 10 m/s^2) 13> A stone of size 1 kg is thrown with a velocity of 20 m/s across the froze surface of a lake and it comes to rest after traveling a distance of 50 m. Wha the force of friction between the stone and the ice?
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Answer:
Given: t=2s, F=1500N, u=30m/s, v=0m/s,
acceleration = (v-u)/t
= (0-30)/2 = -15 m/s^2m/s
2
The negative acceleration just indicates retardation.
Force = mass x acceleration
→ Mass = force/acceleration
→ = 1500/(15)
= 100kg
(a) To find change in momentum
Change in momentum = final velocity – initial velocity or Δp = m(v-u)
Δp = 100(0-30)
= 3000 kg m/s
(b) Retardation produced in car
We know that retardation is negative acceleration
∴acceleration = (v-u)/t
= (0-30)/2 = -15 m/s^2m/s
2
Retardation is 15 m/s^2m/s
2
(c) Mass of the car
As per newton’s second law of motion,
Force = mass x acceleration
→ Mass = Force/acceleration
→ = 1500/15
→ = 100kg
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