Newton 1 Answers

Solution

Q1

The magnitude of the acceleration a is 

a = Fnet / m

a = 51 N  /   24kg

Substituting the units kg ⋅ m/s2 for N yields

a = 51 kg.m/s2  /  24 kg

=  2.1 m/s2

Q2

Fnet = ma,

where Fnet is the net force along the horizontal direction. We can see from Figure 4 that the engine thrusts add, while friction opposes the thrust. In equation form, the net external force is

Fnet = 4T−f.

Substituting this into Newton’s second law gives

Fnet = ma = 4T−f.

Using a little algebra, we solve for the total thrust 4T:

4T = ma + f.

Substituting known values yields

4T = ma + f

= (2100 kg) x  (49 m/s2) + 650 N

So the total thrust is

4T = 1.0 × 10>5 N

and the individual thrusts are

T = 1.0 × 10>5 N / 4

= 2.6 × 10>4 N

Could also do this as Ft (Force of thrust) and then divide by 4 at the end to find individual thrust.

Discussion

The numbers are quite large. Experiments such as this were performed in the early 1960s to test the limits of human endurance and the setup designed to protect human subjects in jet fighter emergency ejections. Speeds of 1000 km/h were obtained, with accelerations of 45 g’s. (45×9.80 m/s2, which is approximately 440 m/s2.) While living subjects are not used any more, land speeds of 10,000 km/h have been obtained with rocket sleds. 

Newton’s second law of motion is more than a definition; it is a relationship among acceleration, force, and mass. It can help us make predictions. Each of those physical quantities can be defined independently, so the second law tells us something basic and universal about nature