AS Physics Forces

Two masses hang at rest from a spring, as shown in the diagram. The string separating the masses is burned through. Which of the following gives the accelerations of the two masses as the string breaks?

acceleration of free fall = g

• A

• B

• C

• D

Which one of the following could not be used as a unit of force?

• A T m

• W s^–2

• kg m s^–2

• J m^–1

A truck of mass 2.1 × 10³ kg tows a car of mass 1.3 × 10³ kg along a horizontal road.

The total resistive force on the car is 1100 N.

The acceleration of the car and truck is 2.3 m s⁻². What is the tension in the tow rope?

• 3000 N

• 4100 N

• 7800 N

• 8900 N

A lift and its passengers with a total mass of 500 kg accelerates upwards at 2 m s^–2 as shown. Assume that g = 10 m s^–2

What is the tension in the cable?

• 1000 N

• 4000 N

• 5000 N

• 6000 N

A parachutist descends to the ground at a constant speed with the parachute open. Which force, together with the parachutist’s weight, makes a pair according to Newton’s third law of motion?

• the drag force on the parachutist from the air

• the tension in the strings of the parachute

• the gravitational force of the parachutist on the Earth

• the lift force on the parachute from the air

A suitcase weighing 200 N is placed on a weighing scale in a lift.

The scale reads 180 N when the lift is moving.

The lift is

• moving down at a constant velocity

• moving down with a decreasing velocity.

• moving up at a constant velocity.

• moving up with a decreasing velocity.

A rocket of mass 12 000 kg accelerates vertically upwards from the surface of the Earth at 1.4 m s⁻².

What is the thrust of the rocket?

• 1.7 × 10⁴ N

• 1.7 × 10⁵ N

• 1.3 × 10⁵ N

• 1.6 × 10⁵ N

A 0.20 kg mass is suspended from a spring. A 0.10 kg mass is suspended from the 0.20 kg mass using a thread of negligible mass.

The system is in equilibrium and the thread is then cut. What is the upward acceleration of the 0.20 kg mass at the instant that the thread is cut?

• 3.3 m s^–2

• 4.9 m s^–2

• 6.5 m s^–2

• 9.8 m s^–2

A lift of mass M is suspended from a cable. The lift descends with a downward acceleration, a. A frictional force F acts on the lift.

What is the tension T in the cable?

• T = Ma + F

• T = Ma – F

• T = M (g + a) – F

• T = M (g – a) – F