Find the mass of the body

CBSE Class 9 CBSE Class 9 Science
1
  1. A force of 30 N produces an acceleration of 2 m/s2 in a body of mass m. Find the mass of the body. Also, find the acceleration, if force is doubled in magnitude along the same direction.
  2. A bullet of mass 10 g strikes a sand bag with the speed of 103 m/s after covering the distance of 5 cm.
    Based on above information, calculate the following:
    • The resistive force exerted by sand on the bullet.
    • The time taken by bullet to come to rest.
2
  1. Given, F = 30 N, a = 2 m/s2
    So, mass of body, m = image = 15 kg [∵ F = ma]
    If f is double, a is double as F ∝ a [since, m is constant]
    So, a = 4m/s2
  2. Given, m = 10 g = 0.01 kg,
    u = 103m/s, v = 0
    s = 5 cm = 0.05 m
    • Acceleration of bullet, a = image [From third equation of motion]
      Force applied by the bullet, F = 0.01 x -107 = - 105N [Negative sign shows direction of force against the direction of motion]
      The resistive force exerted by the sand on the bullet = 105
    • Time taken by bullet to come to rest, t = image = image = 10–4 [From first equation of motion]