Momentum Review

Momentum =

• mass x speed

• mass x velocity

• mass x volume

• force x distance

The equation for momentum is;

• m = pv

• v = mp

• p = mv

• v = pm

A car of mass 1000 kg moves at a speed of 15 m/s east. The car's momentum is

• 15000 N east

• !500 kg m/s east

• 0.015 kg m/s east

• 15000 kg m/s east

A gun of mass 3 kg fires a bullet of mass 0.002 kg at a speed of 700 m/s. At what speed does the rifle recoil?

• 0.23 m/s

• 0.47 m/s

• 1.23 m/s

• 1.54 m/s

Answer explanation

Mv + mV = 0

Mv is momentum of gun, mV is momentum of bullet.

3v + 0.002 x 700 = 0, so 3v = -1.4

v =-1.4/3 = -0.47 m/s

When a collision occurs, between two cars, which of the following is conserved?

• Velocity

• Speed

• Momentum

• Kinetic Energy

Bumper car 1 with momentum 1000 kg m/s, collides with car2 which has momentum - 500kg m/s. After the collision, Car 1 has momentum of 200 kg m/s. What is the momentum of Car 2?

• 100 kg m/s

• 300 kg m/s

• 500 kg m/s

• 700 kg m/s

Answer explanation

Momentum before = 1000 - 500 = 500 kg m/s

Momentum after = 500 kg m/s . If car 1 has 200, car 1 must have the other.

What is the relationship between Force and momentum?

• Momentum = change in force / time

• Momentum = change in time / force

• force = change in time / momentum

• force = change in momentum / time

A bus has momentum 10000 kgm/s. 5.0 s later it has momentum 12500 kg m/s. What is the net force acting on the bus?

• 300 N

• 500 N

• 2500 N

• 5000 N

Answer explanation

Force - Change in momentum/ time = (12500 - 10000)/ 5 = 500N

Conservation of momentum applies to the following situation.

• Isolated systems not acted on by external forces

• The moon orbiting the earth?

• A man fired out of a cannon

• A stone fired from a catapult

Answer explanation

The moon, the man and the stone are all acted on by EXTERNAL forces.

A dart of mass 0.030 kg is fired at a speed of 25 m/s and is embedded in buggy of mass 0.270 kg. What speed will the buggy and the dart have after the collision?

• 1.5 m/s

• 2.0 m/s

• 2.5 m/s

• 3.0 m/s

Answer explanation

Momentum before (and after) = 0.03 x 25 = 0.75 kg m/s. Total mass in motion = 0.3 kg. v = p/m = 2.5 m/s