Further Mechanics Revision

A force acting on a body of mass 2 kg causes its speed to increase from 2ms^-1 to 6ms^-1. Find the average force acting, given that it acts for 2 seconds.

• 8N

• 4N

• 4J

• 6N

A body of mass 1kg is moving with speed 2ms-1. It collides head-on with a body of mass 2kg moving with speed 3ms-1. The two bodies stick together, and move off with velocity v. Find v.

• -1.33ms^-1

• 1.67ms^-2

• 1.33ms^-1

• 1.67N

In an elastic collision.... (click all that apply)

• momentum is conserved

• kinetic energy is conserved

• momentum is lost

• kinetic energy is transferred to other types

In a totally inelastic collision...

• ... momentum changes always.

• ...the collision causes moving bodies to stop.

• .. a force must act.

• ... most of all the kinetic energy is transferred to other types.

State the condition under which the principle of conservation of momentum applies.

• When no external force or energy changes occur.

• When no external force acts only.

• When there are no changes in kinetic energy.

• When the mass of an object is constant.

Momentum must be conserved in both the x and y directions when a bomb explodes (assuming no external forces apply).

• True

• False

What two quantities are conserved in an elastic collision.

• Force and Energy

• Kinetic Energy and mass

• Kinetic Energy and momentum

• Total energy and momentum

A gas molecule makes an elastic collision with the walls of a gas cylinder. The molecule is travelling at 450 m s–1 at right angles towards the wall before the collision. What is the magnitude and direction of its velocity after the collision?

• 450ms^-1 in the opposite direction.

• 450ms^-1 in the same direction.

• 225ms^-1 in the opposite direction.

• 0ms^-1, it stops.

A gas molecule makes an elastic collision with the walls of a gas cylinder. The molecule is travelling at 450 m s^–1 at right angles towards the wall before the collision. Calculate the change in momentum of the molecule during the collision if it has a mass of 8.0 × 10^–26 kg.

• 3.6× 10^–23Ns

• 7.2 × 10^–23Ns

• 3.6 x 10^-26N

• 14.4 × 10^–23Ns

A ball of mass m, which is fixed to the end of a string of length l, is released from X. It swings in a circular path, passing through the lowest point Y at speed u. If the tension in the string at Y is T, which one of the following represents a correct equation at Y?

• T = mu²/l - mg

• T-mg = mu²/l

• mg-T = mu²/l

• T+mu²/l = mg