# MCAT Physical : Newton's Second Law

## Example Questions

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### Example Question #11 : Newton's Second Law

A 2kg lead ball is loaded into a spring cannon and the cannon is set at a 45º angle on a platform. The spring has a spring constant of 100N/m and the ball and spring system is compressed by 1m before launch. While the ball is in flight air resistance can be neglected, and the ball finishes its flight by landing at a cushion placed some distance away from the cannon.

When the ball leaves the cannon, how fast is it traveling?

20m/s

9m/s

5m/s

10m/s

10m/s

Explanation:

Think back to the 3 main kinematics equations that we know:

vf2 = vi2 + 2aΔx

vf = vi + at

Δx = vit + ½at2

Newton’s second law can be used in combination with the spring force equation to solve for the acceleration of the system. Remember that any force, whether it is kinematic, electrical, or gravitational, is equal to Newton’s second law.

Fspring = kx = masystem

Now we need to choose which equation gives us the final velocity, given that we know the acceleration and the change in position (1m).

vf2 = vi2 + 2aΔx

vf= (0 m/s)2 + 2(50 m/s2)(1 m) = 100 m2/s2

### Example Question #3 : Linear Motion

A car moving at 40m/s suddenly applies a braking force and comes to rest in 20s, with constant deceleration. If the car has a mass of 2000kg, what is the braking force?

40000N

4000N

–8000N

–4000N

–2000N

–4000N

Explanation:

First we can calculate the acceleration.

Using F = ma with the magnitude of the acceleration we can find the force.

### Example Question #1 : Newton's Second Law

A 2000kg car with a velocity of  collides head on with a 6000kg truck with a velocity of . Which vehicle experiences the greater force? Which experiences the greater acceleration?

The car experiences the greater force and the greater acceleration

The truck experiences the greater force and the greater acceleration

The car and the truck experience equal force and the car experiences greater acceleration

Both the car and the truck experience equal force and acceleration

The truck experiences the greater force and the car experiences the greater acceleration

The car and the truck experience equal force and the car experiences greater acceleration

Explanation:

The car and the truck experience equal and opposite forces, but since the car has a smaller mass it will experience greater acceleration than the truck according to the equation F = ma.

A greater mass will decrease the acceleration.

### Example Question #61 : Forces

A force of  is applied to a block with a mass of  on a frictionless surface. What is the acceleration of the block?

The block moves with a constant velocity

Explanation:

For this question we must use Newton's second law. We have to use the formula .

is the force being applied,  is the mass of the object, and  is the acceleration of the object

### Example Question #12 : Newton's Second Law

A  cart is pushed so that it moves with a constant acceleration of . What was the force of the push?