Question

The same constant force, F, is applied to two blocks. The first block has a mass of M and the second block has a mass of 2M. Both blocks are initially at rest and the force acts on each of them for the same period of time, t.

15)  After time, t, which block has more momentum?

a)The block of mass M

b)The block of mass 2M

c)They will have the same momentum

16)  After time, t, which block has more kinetic energy?

a)The block of mass M

b)The block of mass 2M

c)They will have the same kinetic energy

17)  After time, t, which block is moving the fastest?

a)The block of mass M

b)The block of mass 2M

c)They will have the same speed

Answer 1

1. From Impulse momentum theorem we can say

$\dpi{100} Impulse = Force * time$

$\dpi{100} P_f - P_i = F*t$

$\dpi{100} P_f - 0 = F*t$

Since force on two blocks are same for same interval of time

So both blocks will have same momentum (C)

2) Relation between KE and Momentum is given by

$\dpi{100} KE = \frac{P^2}{2m}$

so here momentum of two objects are same

so we can say KE is iinversely proportional to mass "m"

so lesser mass more KE

a)The block of mass M will have more KE

3) Now since the two blocks will have same Force so lesser mass block will have more acceleration

$\dpi{100} a = \frac{F}{m}$

So it will gain more speed in same time then the mass "2m"

a)The block of mass M will move faster