In bench pressing 100 kg, a weight lifter applies a force of 1040 N. How large is the upward acceleration of?

Question

the weights during the lift? Can somebody please explain in detail how to get this answer? The answer is 0.60m/s^2.

Answer 1

f=mA

A=f/m

You have to remember that just holding the bar against gravity takes a force so you have to remove this first.

f=100*9.81

=981

So the force that goes into the acceleration is 1040-981

=59N

Therefore the acceleration is

=59/100

=0.59m/s^2

I guess you were supposed to use the less accurate form of the earths acceleration, 9.80m/s^2

Answer 2

You should draw a free body diagram for this, as should be done in all physics problems involving a force.  It allows you to visualize the problem better, and therefore makes it easier.

There are two forces in this problem: the force exerted by the bench press weight and the force exerted by the weight lifter.  The force exerted by the weight lifter is known (1040 N).  The force of the weights are known from F = m*a, where m is the mass of the weights (100 kg) and a is the acceleration from gravity (9.8 m/s^2).

F_weights = 100kg * 9.8m/s^2 = 980 N

So now you have 980 N down and 1040 N up.  Subtract the downward force of the weights from the upwards force of the lifter:

F_net = 1040 N - 980 N = 60 N

Since Force = Mass*Acceleration, and the force is known (60 N) and the mass is known (100 kg), acceleration can be found by: a = F/m

Acceleration = 60N/100kg = 0.6 m/s^2 upward

Answer 3

Force = mass x acceleration

if the you know the force and mass, rearrange the equation to give,

Acceleration = Force / Mass

This should roughly give you an acceleration of 10.4m/s^2, then you must deduct the acceleration due to gravity (because it is in the opposite direction to the lift), which I'd approximate at 9.8m/s^2, giving you a total acceleration of 0.6m/s^2