Forces Practice Questions

Define the weight of an object.

Calculate the weight of the bag of sand.

weight = ............................................... N

Describe how the weight of the bag of sand could be measured in the workshop.

State Newton's first law.

State the size of the total resistive force acting on the cyclist.

resistive force = ............................................... N

The cyclist then increases the forward force to $160$ N. The resistive force stays the same.

Describe the effect this has on the motion of the cyclist.

State the name of the force that provides the centripetal force on the ball.

State the direction of the resultant force acting on the ball.

The string suddenly breaks. Describe the motion of the ball immediately after the string breaks.

Calculate the weight of the rocket.

weight = ............................................... N

Calculate the resultant force on the rocket at the moment of launch.

resultant force = ............................................... N

Calculate the acceleration of the rocket at the moment of launch.

acceleration = ............................................... m/s$^2$

Describe how the student should change the mass of the moving system in this investigation, while keeping the accelerating force constant.

Describe how the student could use light gates to find the acceleration of the trolley.

The student plots a graph of acceleration against $\frac{1}{\text{mass of the moving system}}$.

State the shape of the line the student should expect and explain what this shows.

The student's graph of acceleration against accelerating force is a straight line, but the line does not pass through the origin.

Explain what this tells the student about the forces acting on the trolley.

Use the results in the table to calculate the gradient of the line, and use your value to calculate the total mass of the moving system.

mass = ............................................... kg

The student repeats the experiment with the runway tilted slightly, so that the trolley rolls down it at a constant speed when given a gentle push.

State the effect this has on the graph.

State Newton's third law.

The Earth pulls the person downwards with a force of $600$ N.

State the force that forms a Newton's third law pair with this force.

The floor of the lift pushes upwards on the person with a force of $600$ N.

Explain why this force is not the Newton's third law pair of the person's weight.

Calculate the mass of the space probe.

mass = ............................................... kg

Calculate the weight of the space probe when it is standing on the surface of Mars.

weight = ............................................... N

The probe then travels to Titan.

Describe what happens to the mass and to the weight of the probe.

State the resultant vertical force on the crate and explain what this tells you about the vertical motion of the crate.

Calculate the acceleration of the crate.

acceleration = ............................................... m/s$^2$

The pulling force is then reduced to $90$ N. The frictional force stays at $90$ N.

Describe the motion of the crate after the pulling force has been reduced.

A skydiver of mass $75$ kg jumps from a helicopter that is hovering high above the ground. She falls for several seconds before opening her parachute, and then lands safely.

Explain how the forces acting on the skydiver determine her motion from the moment she leaves the helicopter until she lands.

Use Newton's first law and Newton's second law in your answer.

Calculate the size of the force acting on skater A during the push.

force = ............................................... N

State the size and direction of the force acting on skater B during the push. Justify your answer.

Calculate the acceleration of skater B during the push.

acceleration = ............................................... m/s$^2$

Explain why the car is accelerating, even though its speed is constant.

Calculate the acceleration of the car.

acceleration = ............................................... m/s$^2$

Ice forms on part of the track, greatly reducing the friction between the tyres and the road.

Explain, using Newton's first law, what happens to the car as it reaches the icy part of the track.